A
abiotic component
Any non-living chemical or physical part of the environment that affects living organisms and the functioning of ecosystems, such as the atmosphere and water resources.
abscission
The shedding of flowers, leaves, and/or fruit following formation of scar tissue in a plant.
absorption
A process in which one substance permeates another. A fluid permeates or is dissolved by a liquid or solid. Skin absorption is a route by which substances can enter the body through the skin.
absorption spectrum
The spectrum of electromagnetic radiation that has passed through a medium which absorbs radiation of certain wavelengths.
acclimatization
Adaptation to a new climate, as with a new temperature or altitude or environment.
acetyl-CoA
A molecule that participates in many biochemical reactions in protein, carbohydrate, and lipid metabolism, notably the citric acid cycle.
acoelomate
A type of animal, such as a flatworm or a jellyfish, with a body plan that lacks a fluid-filled cavity between the body wall and the digestive tract. Rather, semi-solid mesodermal tissues between the gut and body wall hold the animal's organs in place. Contrast coelomate and pseudocoelomate.
action potential
The local change in voltage that occurs when the membrane potential of a specific location along the membrane of a cell rapidly depolarizes, such as when a nerve impulse is transmitted between neurons.
activation energy
The energy that an atomic system must acquire before a process (such as an emission or reaction) can occur.
active site
The part of an enzyme or antibody at which substrate molecules bind and undergo a chemical reaction.
active transport
Transport of a substance (such as a protein or drug) across a cell membrane against a concentration gradient. Unlike passive transport, active transport requires an expenditure of energy.
adaptation
adaptive radiation
The process by which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, creates new challenges, or opens new niches.
adenine
A purine-derived organic compound which is one of the four canonical nucleobases used in the nucleic acids DNA and RNA. Its derivatives are involved in a wide variety of biochemical reactions, including cellular respiration.
adenosine triphosphate (ATP)
An organic compound derived from adenine that functions as the major source of energy for chemical reactions inside living cells. It is found in all forms of life and is often referred to as the "molecular currency" of intracellular energy transfer.
adipose tissue
A type of loose connective tissue made of mostly adipocytes and found in human and animal tissue, where it is colloquially known as body fat.
aerobic
Capable of surviving and growing in the presence of oxygen.
aerobiology
The study of organic particles which are passively transported by the air, including bacteria, fungal spores, very small insects, pollen grains, and viruses.
agriculture
The practice of cultivating land, growing food, and/or raising livestock.
agrobiology
The study of plant nutrition and growth, especially as a way to increase crop yield.
alga
(pl.) algae
Any member of a diverse polyphyletic group of photosynthetic, eukaryotic, mostly aquatic organisms ranging from simple unicellular microalgae to massive colonial or multicellular forms such as kelp. Algae may reproduce sexually or asexually, and are often compared to plants, though they lack most of the complex cell and tissue types that characterize true plants.
allopatric speciation
A form of speciation which occurs when biological populations of the same species become isolated from each other to an extent that prevents or interferes with genetic interchange.
amino acid
A class of organic compounds containing an amine group and a carboxylic acid group which function as the fundamental building blocks of proteins and play important roles in many other biochemical processes.
amniote
An organism which produces an egg composed of a shell and membranes that creates a protected environment in which the embryo can develop outside of water.
anaerobic
analogous structures
A set of morphological structures in different organisms which have similar form or function but were not present in the organisms' last common ancestor. The cladistic term for the same phenomenon is homoplasy.
anatomy
The branch of biology that studies the structure and morphology of living organisms and their various parts.
animal
Any member of a clade of multicellular eukaryotic organisms belonging to the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, reproduce sexually, and grow from a blastula during embryonic development. An estimated 7 million distinct animal species currently exist.
antibiotic
Also called an antibacterial.
A type of antimicrobial drug used in the treatment and prevention of bacterial infections.
apoptosis
A highly regulated form of programmed cell death that occurs in multicellular organisms.
arachnology
The scientific study of spiders, scorpions, pseudoscorpions, and harvestmen, collectively called arachnids.
archaea
artificial selection
Also called selective breeding.
The process by which humans use animal breeding and plant breeding to selectively control the development of particular phenotypic traits in organisms by choosing which individual organisms will reproduce and create offspring. While the deliberate exploitation of knowledge about genetics and reproductive biology in the hope of producing desirable characteristics is widely practiced in agriculture and experimental biology, artificial selection may also be unintentional and may produce unintended (desirable or undesirable) results.
asexual reproduction
A type of reproduction involving a single parent that results in offspring that are genetically identical to the parent.
astrobiology
The branch of biology concerned with the effects of outer space on living organisms and the search for extraterrestrial life.
autoimmunity
The system of immune responses of an organism directed against its own healthy cells and tissues.
autotroph
Sometimes used interchangeably with primary producer.
An organism capable of producing complex organic compounds from simple substances present in its surroundings, generally by using energy from sunlight (as in photosynthesis) or from inorganic chemical reactions (as in chemosynthesis). Autotrophs do not need to consume another living organism in order to obtain energy or organic carbon, as opposed to heterotrophs.
B
B cell
A type of lymphocyte in the humoral immunity of the adaptive immune system.
bacteria
An enormous and diverse clade of microscopic, prokaryotic, single-celled organisms which lack a true nucleus. They represent one of the three fundamental biological domains.
bacteriophage
A virus that infects and multiplies within bacteria.
Barr body
The inactive X chromosome in a female somatic cell, rendered inactive in a process called lyonization, in those species in which sex is determined by the presence of the Y chromosome (including humans) or W chromosome rather than by the presence of two X chromosomes or two Z chromosomes.
basal body
An organelle formed from a centriole, and a short cylindrical array of microtubules. Also called a basal granule, a kinetosome, and in older cytological literature, a blepharoplast.
behavioral ecology
The study of the evolutionary basis for animal behavior due to ecological pressures.
bile
A dark green to yellowish-brown fluid, produced by the liver of most vertebrates, which aids the digestion of lipids in the small intestine. Also called gall.
binary fission
The process by which one prokaryotic cell divides into two identical daughter cells.
binomial nomenclature
A formal system of classifying species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages.
biocatalysis
The process of catalysis in biological systems. In biocatalytic processes, natural catalysts, such as protein enzymes, perform chemical transformations on organic compounds.
biochemistry
The branch of biology that studies the chemical properties, compositions, reactions, and processes related to living organisms.
biodiversity
A contraction of "biological diversity" generally referring to the variety and variability of life on Earth.
bioengineering
The application of concepts and methods of biology to solve real-world problems related to the life sciences or the application thereof.
bioenergetics
The study of the transformation of energy within and between living organisms.
biogeography
The study of the distribution of species and ecosystems in geographic space and through geological time. Organisms and biological communities often vary in a regular fashion along geographic gradients of latitude, elevation, isolation and habitat area.
bioinformatics
The application of computer technology to the management of biological information.
biological organization
The hierarchy of complex biological structures and systems, designed to define life through a reductionist approach.
biology
The study of life and living organisms.
biomass
Organic matter derived from living or recently living organisms. Biomass can be used as a source of energy and it most often refers to plants or plant-based materials which are not used for food or feed, and are specifically called lignocellulosic biomass.
biomathematics
The theoretical use of mathematical models and abstractions of living systems to understand and predict biological problems.
biome
Any very large ecological area on the Earth's surface containing fauna and flora (animals and plants) adapting to their environment. Biomes are often defined by abiotic factors such as climate, topographical relief, geology, soils, and water resources.
biomechanics
The study of the structure and function of biological systems by means of the methods of "mechanics", which is the branch of physics involving analysis of the actions of forces.
biomedical engineering
The application of engineering principles and design concepts to medicine and biology for healthcare purposes (e.g. diagnostic or therapeutic).
biomedical research
The pursuit of answers to medical questions. These investigations lead to discoveries, which in turn lead to the development of new preventions, therapies, and cures for problems in human and veterinary health. Biomedical research generally takes two forms: basic science and applied research.
biomolecule
Molecules and ions that are present in organisms, essential to some typically biological process such as cell division, morphogenesis, or development.
biophysics
The application of approaches traditionally employed in physics to study biological systems.
biosynthesis
biotechnology
Biotechnology is the use of living systems and organisms to develop or make products, or "any technological application that uses biological systems, living organisms or derivatives thereof, to make or modify products or processes for specific use" (UN Convention on Biological Diversity).
bipedal
A form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs.
birth
blastocyst
A mammalian blastula in which some differentiation of cells has occurred.
blood
A body fluid that circulates in humans and other vertebrate animals and is generally responsible for delivering necessary substances such as oxygen and nutrients between the cells and tissues of the body and transporting metabolic waste products away from those same cells and tissues.
blood-brain barrier
A semipermeable membrane separating the blood from the cerebrospinal fluid, and constituting a barrier to the passage of cells, particles, and large molecules.
botany
The branch of biology that studies plants.
building biology
A science that leads to natural healthy ecological homes, schools, and workplaces that exist in harmony with the environment.
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C
Calvin cycle
Also called the biosynthetic phase, light-independent reactions, dark reactions, or photosynthetic carbon reduction (PCR) cycle.
A series of chemical reactions which occurs as one of two primary phases of photosynthesis, specifically the phase in which carbon dioxide and other compounds are converted into simple carbohydrates such as glucose. These reactions occur in the stroma, the fluid-filled area of the chloroplast outside the thylakoid membranes. In the Calvin cycle, the products of previous light-dependent reactions (ATP and NADPH) undergo further reactions which do not require the presence of light and which can be broadly divided into three stages: carbon fixation, reduction reactions, and ribulose 1,5-bisphosphate (RuBP) regeneration.[1]
carbon fixation
Also called carbon assimilation.
The process by which inorganic carbon, particularly in the form of carbon dioxide, is converted to organic compounds by living organisms. Examples include photosynthesis and chemosynthesis.
carbonate
Any member of two classes of chemical compounds derived from carbonic acid or carbon dioxide.
carotenoid
One of a class of organic pigments produced by algae and plants, as well as certain bacteria and fungi.
catalase
An enzyme found in nearly all living organisms exposed to oxygen, including bacteria, plants, and animals.
cell
The basic structural and functional unit of all living organisms, and the smallest functional unit of life. A cell may exist as an independent, self-replicating unit (as in the case of unicellular organisms), or in cooperation with other cells, each of which may be specialized for carrying out particular functions within a larger multicellular organism. Cells consist of cytoplasm enclosed within a cell membrane and sometimes a cell wall, and serve the fundamental purpose of separating the controlled environment in which biochemical processes take place from the outside world. Most cells are visible only under a microscope.
cell biology
Also called cytology.
The branch of biology that studies the structure and function of living cells, including their physiological properties, metabolic processes, chemical composition, life cycle, the organelles they contain, and their interactions with their environment. This is done at both microscopic and molecular levels.
cell cycle
The ordered series of events which take place in a cell leading to duplication of its genetic material and ultimately the division of the cytoplasm and organelles to produce two or more daughter cells. These events can be broadly divided into phases of growth and division, each of which can vary in duration and complexity depending on the tissue or organism to which the cell belongs. Cell cycles are essential processes in all unicellular and multicellular organisms.
cell division
Any process by which a parent cell divides into two or more daughter cells. Examples include binary fission, mitosis, and meiosis.
cell membrane
The semipermeable membrane surrounding the cytoplasm of a cell.
cell nucleus
The "control room" for the cell. The nucleus gives out all the orders.
cell plate
Grown in the cell's center, it fuses with the parental plasma membrane, creating a new cell wall that enables cell division.
cell theory
The theory that all living things are made up of cells.
cell wall
A tough, often rigid structural barrier surrounding certain types of cells (such as in fungi, plants, and most prokaryotes) that is immediately external to the cell membrane.
cellular
Of or relating to a cell.
central dogma of molecular biology
A framework for understanding the movement of genetic information between information-carrying biopolymers within biological systems. Popularly (though simplistically) stated as "DNA makes RNA and RNA makes protein", the principle attempts to capture the notion that the transfer of genetic information only naturally occurs between certain classes of molecules and in certain directions.
centriole
A cylindrical cell structure found in most eukaryotic cells, composed mainly of a protein called tubulin.
centrosome
An organelle that is the primary site at which microtubules are organized. They occur only in plant and animal cells and help to regulate cell division.
chemical compound
A chemical substance consisting of two or more different chemically bonded elements, with a fixed ratio determining the composition. The ratio of each element is usually expressed by a chemical formula.
chemical equilibrium
The state in which both reactants and products are present in concentrations which have no further tendency to change with time in a chemical reaction.
chemical reaction
A process that leads to the transformation of one set of chemical substances to another.
chemistry
A branch of the physical sciences that studies the composition, structure, properties, and change of matter. Chemical interactions underlie all biological processes.
chemosynthesis
chlorophyll
Any of several photosynthetic pigments found in cyanobacteria, algae, or plants.
chloroplast
A type of highly specialized organelle in the cells of plants and algae, the main role of which is to conduct photosynthesis, by which the photosynthetic pigment chlorophyll captures the energy from sunlight and converts and stores it in the molecules ATP and NADPH while freeing oxygen from water.
cholesterol
A type of lipid molecule that is biosynthesized by all animal cells because it is an essential structural component of animal cell membranes, essential for maintaining both membrane structural integrity and fluidity.
chromosome
A threadlike strand of DNA in the cell nucleus that carries the genes in a linear order.
cilia
circadian rhythm
citric acid cycle
Also called the Krebs cycle and tricarboxylic acid cycle (TCA).
A series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins into carbon dioxide and chemical energy in the form of guanosine triphosphate (GTP). In addition, the cycle provides the chemical precursors for certain amino acids as well as the reducing agent NADH that is used in numerous other biochemical reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest established components of cellular metabolism and may have originated abiogenically.
clade
class
clonal selection
A scientific theory in immunology that explains the functions of cells (lymphocytes) of the immune system in response to specific antigens invading the body. The theory has become the widely accepted model for how the immune system responds to infection and how certain types of B and T lymphocytes are selected for destruction of specific antigens.[2]
cloning
The process of producing individual organisms or molecules with identical or virtually identical DNA, either naturally or artificially. Many organisms, such as bacteria, insects, and plants, are capable of naturally producing clones through asexual reproduction. In biotechnology, cloning refers to the artificial creation of copies of cells, DNA fragments, or other biomolecules by various laboratory techniques.
coat, coating
In the context of virus capsid, may refer colloquially to the defined geometric structure of a capsid, or the membrane of an endosome containing an intact virion. The coat of a virus is used in descriptions for the general public. Related slang: uncoating.
colony
comparative biology
The use of comparative methods to study the similarities and differences between two or more biological organisms (e.g. two organisms from the same time period but different taxa, or two organisms from the same taxon but different times in evolutionary history). The side-by-side comparison of morphological or molecular characteristics of different organisms is the basis from which biologists infer the organisms' genetic relatedness and their natural histories. It is a fundamental tool in many biological disciplines, including anatomy, physiology, paleontology, and phylogenetics.
conservation biology
The scientific study of nature and of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction and the erosion of biotic interactions.
convergent evolution
An evolutionary process by which species of different lineages independently develop similar characteristics, often to the point that the species appear to be more closely related than they actually are.
countercurrent exchange
The crossover of some property, usually heat or some component, between two fluids flowing in opposite directions to each other. The phenomenon occurs naturally but is also frequently mimicked in industry and engineering.
crista
A fold in the inner membrane of a mitochondrion.
cryobiology
The branch of biology that studies the effects of low temperatures on living things within Earth's cryosphere or in laboratory experiments.
cytology
See cell biology.
cytoplasm
All of the material within a cell and enclosed by the cell membrane, except for the nucleus. The cytoplasm consists mainly of water, the gel-like cytosol, various organelles, and free-floating granules of nutrients and other biomolecules.
cytosine
One of the four main nitrogenous bases found in both DNA and RNA, along with adenine, guanine, thymine, and uracil (in RNA); it is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group at position 2).
cytoskeleton
A complex, dynamic network of interlinking protein filaments that extends from the cell nucleus to the cell membrane and which is present in the cytoplasm of all cells, including bacteria and archaea.[3] The cytoskeletal systems of different organisms are composed of similar proteins. In eukaryotes, the cytoskeletal matrix is a dynamic structure composed of three main proteins, which are capable of rapid growth or disassembly dependent on the cell's requirements.[4]
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D
Darwinian fitness
The genetic contribution of an individual to the next generation's gene pool relative to the average for the population, usually measured by the number of offspring or close kin that survive to reproductive age.
deciduous
Deciduous means "falling off at maturity" or "tending to fall off", and it is typically used in botany in order to refer to trees or shrubs that lose their leaves seasonally (most commonly during autumn) and to the shedding of other plant structures such as petals after flowering or fruits when ripe.
decomposition
dehydration reaction
A chemical reaction that involves the loss of a water molecule from the reacting molecule.
denaturation
A process in which proteins or nucleic acids lose the quaternary, tertiary, and secondary structure which is present in their native state, when exposed to some external stress or chemical compound such as a strong acid or base, a concentrated inorganic salt, or an organic solvent.
dendrite
A short branched extension of a nerve cell, along which impulses received from other cells at synapses are transmitted to the cell body.
denitrification
The microbially facilitated process of nitrate reduction that ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. It is performed by a large group of heterotrophic facultative anaerobic bacteria and is a fundamental component of the nitrogen cycle.
deoxyribonucleic acid (DNA)
A nucleic acid polymer that serves as the fundamental hereditary material in all living organisms. Each DNA molecule is composed of long sequences of nucleotides, each of which includes one of four nitrogenous bases – adenine (abbreviated A), cytosine (C), guanine (G), and thymine (T) – attached to a sugar-phosphate complex which acts as a "backbone" for the long-chain polymer. DNA most commonly occurs in "double-stranded" form, i.e. as a pair of nucleotide polymers bound together by complementary base pairing.
depolarization
The process of reversing the charge across a cell membrane (such as that of a neuron), thereby causing an action potential. In depolarization, the inside of the membrane, which is normally negatively charged, becomes positive and the outside becomes negative. This is brought about by positively charged sodium ions rapidly passing into the axon.
desmosome
Also called the macula adhaerens.
A cell structure specialized for cell-to-cell adhesion.
developmental biology
The branch of biology that studies the processes by which living organisms grow and develop over time. The field may also encompass the study of reproduction, regeneration, metamorphosis, and the growth and differentiation of stem cells in mature tissues.
disease
Any particular abnormal condition that negatively affects the structure or function of all or part of a living organism and that is not the result of any immediate external injury. Diseases are medical conditions that are often identifiable by specific signs and symptoms. They may be caused by external factors such as infectious pathogens or by internal dysfunctions such as immune deficiency or senescence.
DNA
See deoxyribonucleic acid.
DNA replication
The chemical duplication or copying of a DNA molecule; the process of producing two identical copies from one original DNA molecule, in which the double helix is unwound and each strand acts as a template for the next strand. Complementary nucleotide bases are matched to synthesize the new partner strands.
DNA sequencing
The process of determining the precise order of nucleotides within a DNA molecule.
drug
Any substance that causes a change in an organism's physiology or psychology when consumed. Drugs may be naturally occurring or artificially produced, and consumption may occur in a number of different ways. Drugs are typically distinguished from substances that provide nutritional support such as food.
dimorphism
The existence of a morphological distinction between organisms of the same species, such that individuals of that species occur in one of two distinct forms which differ in one or more characteristics, such as colour, size, shape, or any other phenotypic trait. Dimorphism based on sex – e.g. male vs. female – is common in sexually reproducing organisms such as plants and animals.
dynein
A motor protein in cells which converts the chemical energy contained in ATP into the mechanical energy of movement.
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E
ecological efficiency
The efficiency with which energy is transferred from one trophic level to the next. It is determined by a combination of efficiencies relating to organismic resource acquisition and assimilation in an ecosystem.
ecological pyramid
Also called a trophic pyramid, eltonian pyramid, energy pyramid, or sometimes food pyramid.
A graphical representation of the biomass or bio-productivity generated at each trophic level in a given ecosystem.
ecological succession
The more or less predictable and orderly set of changes that occurs in the composition or structure of an ecological community over time.
ecology
The scientific analysis and study of interactions between organisms and their environment. It is an interdisciplinary field that combines concepts from biology, geography, and Earth science.
ecophysiology
A biological discipline that studies the adaptation of an organism's physiology to environmental conditions.
ecosystem
A community of living organisms in conjunction with the non-living components of their physical environment, interacting as a system.
ecotype
Sometimes called an ecospecies.
In evolutionary ecology, a genetically distinct geographic variety, population, or race within a species which is adapted to specific environmental conditions.
ectoderm
The outermost layer of cells or tissue of an embryo in early development, or the parts derived from this, which include the epidermis, nerve tissue, and nephridia.
ectotherm
An organism in which internal physiological sources of heat are of relatively small or quite negligible importance in controlling body temperature compared to ambient sources of heat. Ectotherms generally experience changes in body temperature that closely match changes in the temperature of their environment; colloquially, these organisms are often referred to as "cold-blooded". Contrast endotherm.
effector
A small molecule that selectively binds to a protein and regulates its biological activity. In this manner, effector molecules act as ligands that can increase or decrease enzyme activity, gene expression, or cell signaling.
efferent
Conducted or conducting outwards or away from something (for nerves, the central nervous system; for blood vessels, the organ supplied). Contrast afferent.
egg
The organic vessel containing the zygote in which an animal embryo develops until it can survive on its own, at which point the developing organism emerges from the egg in a process known as hatching.
electrochemical gradient
A gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts: the electrical potential and the difference in chemical concentration across the membrane.
electron acceptor
Any chemical entity that accepts electrons transferred to it from another chemical entity. It is an oxidizing agent that, by virtue of its accepting electrons, is itself reduced in the process. Contrast electron donor.
electron carrier
Any of various molecules that are capable of accepting one or two electrons from one molecule and donating them to another in the process of electron transport. As the electrons are transferred from one electron carrier to another, their energy level decreases, and energy is released.
electron donor
A chemical entity that donates electrons to another chemical entity. It is a reducing agent that, by virtue of its giving up its electrons, is itself oxidized in the process. Contrast electron acceptor.
electron microscope
A type of microscope that uses a beam of electrons to create an image of a sample or specimen. Electron microscopes are capable of much higher magnifications and have greater resolving power than conventional light microscopes, allowing them to see much smaller objects in finer detail.
electron transport chain
The process of oxidative phosphorylation, by which the NADH and succinate generated by the citric acid cycle are oxidized and electrons are transferred sequentially down a long series of proteins, ultimately to the enzyme ATP synthase, which uses the electrical energy to catalyze the synthesis of ATP by the addition of a phosphate group to ADP. The process takes place in the cell's mitochondria and is the primary means of energy generation in most eukaryotic organisms.
embryo
A developing stage of a multicellular organism.
embryology
The branch of biology that studies the development of gametes (sex cells), fertilization, and development of embryos and fetuses. Additionally, embryology involves the study of congenital disorders that occur before birth.
endangered species
Any species which is very likely to become extinct in the near future, either worldwide or in a particular area. Such species may be threatened by factors such as habitat loss, hunting, disease, and climate change, and most have a declining population or a very limited range.
endemism
The ecological state of an organism or species being unique to a defined geographic location, such as an island, nation, country, habitat type, or other defined zone. Organisms are said to be endemic to a place if they are indigenous to it and found nowhere else.
endergonic reaction
Also called a nonspontaneous reaction or unfavorable reaction.
A type of chemical reaction in which the standard change in free energy is positive, and energy is absorbed.
endocrine gland
A gland of the animalian endocrine system that secretes hormones directly into the blood rather than through a duct. In humans, the major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, hypothalamus, and adrenal glands.
endocrine system
The collection of glands that produce hormones which regulate metabolism, growth and development, tissue function, and a wide variety of other biological processes.
endocytosis
A form of active transport in which a cell transports molecules such as proteins into the cell's interior by engulfing them in an energy-consuming process.
endoderm
One of the three primary germ layers in the very early human embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer), with the endoderm being the innermost layer.
endogenous
(of a substance or process) Originating from within a system (such as an organism, tissue, or cell), as with endogenous cannabinoids and circadian rhythms. Contrast exogenous.
endoplasmic reticulum
A type of organelle found in eukaryotic cells that forms an interconnected network of flattened, membrane-enclosed sacs or tube-like structures known as cisternae.
endosperm
The tissue produced inside the seeds of most of the flowering plants following fertilization.
endosymbiotic theory
Also called symbiogenesis.
An evolutionary theory regarding the origin of eukaryotic cells from a hypothetical internal symbiosis between prokaryotic organisms, first articulated in 1905 and 1910 by the Russian botanist Konstantin Mereschkowski, and advanced and substantiated with microbiological evidence by Lynn Margulis in 1967.
endotherm
An organism that is capable of maintaining a consistent, metabolically favorable body temperature, largely by the recycling of heat released by its internal physiological functions, instead of by relying on ambient sources of heat. Endotherms are generally able to maintain a stable body temperature despite changes in the temperature of their environment; colloquially, these organisms are often referred to as "warm-blooded". Contrast ectotherm.
entomology
The scientific study of insects.
environmental biology
The branch of biology concerned with the relations between organisms and their environments.
enzyme
A protein that acts as a biological catalyst by accelerating chemical reactions. Metabolic pathways depend upon enzymes to catalyze their individual steps, and almost all metabolic processes require enzyme catalysis in order to occur at rates fast enough to sustain life.
epidemiology
The study and analysis of the patterns, causes, and effects of health and disease conditions in defined populations. It is the cornerstone of public health, and shapes policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive healthcare.
epigenetics
A sub-field of genetics that studies cellular and physiological phenotypic trait variations caused by external or environmental factors which affect how cells express genes, as opposed to those caused by changes in the DNA sequence.
epiphyte
An organism that grows on the surface of a plant and derives moisture and nutrients from the air, rain, marine environments, or from debris accumulating around it.
essential nutrient
A nutrient required for normal physiological function which cannot be synthesized by a particular organism, either at all or in sufficient quantities, and which therefore must be obtained from external sources such as food. In humans, a set of nine amino acids, two fatty acids, thirteen vitamins, and fifteen minerals are considered essential nutrients.
estrogen
The primary female sex hormone.
ethology
The scientific study of non-human animal behaviour (i.e. excluding human behaviour) and usually with a focus on behaviour under natural conditions, and viewing behaviour as an evolutionarily adaptive trait.
eukaryote
A type of organism consisting of cells which have a nucleus enclosed within a distinct nuclear membrane, unlike prokaryotes. Eukaryotes include all organisms except the bacteria and archaea (i.e. all plants, animals, fungi, and protists are eukaryotes).
evolution
The change in the heritable characteristics of populations of biological organisms over successive generations, which may occur by mutation, gene flow, natural selection, or random chance.
evolutionary biology
The subfield of biology that studies evolution and the evolutionary processes that produced the diversity of life on Earth from a hypothesized single common ancestor. These processes include the descent of species and the origin of new species.
exocytosis
A form of active transport and bulk transport in which a cell transports molecules out of the cell by expelling them through an energy-dependent process.
exogenous
(of a substance or process) Originating outside of or external to a system (such as an organism, tissue, or cell), as with drugs and many pathogens. Contrast endogenous.
exponential growth
It is exhibited when the rate of change of the value of a mathematical function is proportional to the function's current value, resulting in its value at any time being an exponential function of time.
external fertilization
A type of fertilization in which a sperm unites with an egg external to the body or bodies of the parent organisms. Contrast internal fertilization.
extinction
The termination of the existence of a particular kind of organism or a particular taxon, often a species, as a result of the death of the last individual of the taxon (though the capacity to breed and recover may have been lost before this point, rendering the taxon functionally extinct).
extracellular
Of or occurring in the space outside the plasma membrane of a cell. Contrast intracellular.
extranuclear inheritance
A transmission of genes that takes place outside the nucleus.
F
facultative anaerobe
An organism which is capable of producing energy through aerobic respiration and then switching to anaerobic respiration depending on the amounts of oxygen and fermentable material in the environment.
family
fermentation
A metabolic process that consumes sugar in the absence of oxygen.
fitness
fitness landscape
fertilization
fetus
Also spelled foetus.
An animal embryo after eight weeks of development.
flagellum
(pl.) flagella
A lash-like appendage that protrudes from the cell body of certain bacterial and eukaryotic cells.
flavin adenine dinucleotide (FAD)
A redox cofactor, more specifically a prosthetic group of a protein, involved in different important enzymatic reactions in metabolism.
food chain
The chain of eating and getting nutrition which starts from a small herbivores animal and ends up at a big carnivorous organism.
founder effect
A loss of genetic variation that takes places when a new population is established by a very small number of individuals from a larger population.
fungi
Contents:
0–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z See also References External links
G
G protein
A family of proteins that act as molecular switches inside cells, and are implicated in transmitting signals from a diversity of stimuli outside a cell to its interior.
gamete
gene
Any segment of DNA that contains the information necessary to produce a functional RNA and/or protein product in a controlled manner. Genes are often considered the fundamental molecular units of heredity. The transmission of genes from a parent cell or organism to its offspring is the basis of the inheritance of phenotypic traits.
gene pool
A set of all genes, or genetic information, in any population, usually of a particular species.
generation
genetic code
A set of rules used by living cells to translate information encoded within genetic material (DNA or mRNA sequences) into proteins.
genetic drift
An alteration in the frequency of an existing gene variant in a population due to random sampling of organisms.
genetic variation
Variations of genomes between members of species, or between groups of species thriving in different parts of the world as a result of genetic mutation. Genetic diversity in a population or species is a result of new gene combinations (e.g. crossing over of chromosomes), genetic mutations, genetic drift, etc.
genetics
The study of heredity.
genome
The entire set of genetic material contained within the chromosomes of an organism, organelle, or virus.
genotype
Part of the genetic makeup of a cell, and therefore of an organism or individual, which determines one of its characteristics (phenotype).
genus
gizzard
An organ found in the digestive tract of some animals, including archosaurs (pterosaurs, crocodiles, alligators, and dinosaurs, including birds), earthworms, some gastropods, some fish, and some crustaceans.
guanine
One of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA).
Contents:
0–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z See also References External links
H
habitat
A place for animals, people, and plants and non-living things.
habituation
A form of learning in which an organism decreases or desists its responses to a stimulus after repeated or prolonged presentations .
heredity
The passing on of phenotypic traits from parents to their offspring, either through sexual or asexual reproduction. Offspring cells and organisms are said to inherit the genetic information of their parents.
hermaphrodite
A sexually reproducing organism with both male and female reproductive organs.
herpetology
The branch of zoology that studies reptiles and amphibians.
heterosis
The improved or increased function of any biological quality in a hybrid offspring.
heterotroph
histology
The study of the microscopic anatomy of cells and tissues of plants and animals.
hormone
Any member of a class of signaling molecules produced by glands in multicellular organisms that are transported by the circulatory system to target distant organs to regulate physiology and behaviour.
host
Any living organism that harbors another living organism (known as a "guest" or symbiont), whether the guest is parasitic, mutualistic, or commensalist in its interactions with the host. The guest typically receives shelter and nourishment from the host.
hybrid
hydrocarbon
An organic compound consisting entirely of hydrogen and carbon atoms. Hydrocarbons from which one hydrogen atom has been removed are functional groups called hydrocarbyls.
I
ichthyology
The branch of biology devoted to the study of fish, including bony fishes (Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha).
immune response
The immune response is how your body recognizes and defends itself against bacteria, viruses, and substances that appear foreign and harmful.
immunity
immunoglobulin
Any of a class of glycoprotein molecules produced by plasma cells (white blood cells) which act as a critical part of the immune response by specifically recognizing and binding to particular antigens, such as bacteria or viruses, and aiding in their destruction. They are a major component of the group of immune defense molecules collectively called antibodies.
infection
The invasion of an organism's cells or tissues by a disease-causing pathogen, its growth and/or multiplication, and the reaction of the host organism to the infectious agent and the toxins it produces. The variety of biological pathogens capable of causing infections includes certain bacteria, viruses, fungi, protists, parasitic worms, and arthropods.
insulin
An anabolic peptide hormone produced in the pancreas which helps to regulate the metabolism of carbohydrates, fats, and protein by promoting the absorption of glucose from the blood into liver, fat, and skeletal muscle cells. Abnormal insulin activity is the cause of diabetes mellitus.
integrative biology
The various forms of cross-disciplinary and multitaxon research.
interferon
A group of signaling proteins made and released by host cells in response to the presence of several pathogens, such as viruses, bacteria, parasites, or tumor cells. In a typical scenario, a virus-infected cell will release interferons causing nearby cells to heighten their antiviral defenses.
internal fertilization
A type of fertilization which takes place inside the egg-producing individual.
International System of Units
(French: Système international d'unités; abbreviated SI) The modern standardized form of the metric system of units and measurements, and the system of measurement formally adopted for use in the physical and natural sciences.
interphase
intracellular
Of or occurring inside or within the enclosed interior of a cell. Contrast extracellular.
introduced species
Also called an exotic species, foreign species, alien species, non-native species, or non-indigenous species.
Any species living outside its native geographic range, and which has arrived there either by accidental or deliberate human activity. Such human-caused introduction of species to foreign environments is distinguished from biological colonization, by which species spread to new areas through "natural" means (i.e. without the involvement of humans).
invertebrate
A group of animals that have no backbone, unlike animals such as reptiles, amphibians, fish, birds, and mammals, which all have a backbone. Among the many extant invertebrate phyla are the Cnidaria, Mollusca, Annelida, Nematoda, and Arthropoda.
ion
An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.
ionic bond
A type of chemical bond involving the complete transfer of valence electron(s) between two atoms. Such bonds typically occur between elements characterized as metals and nonmetals, and generate two oppositely charged ions: the metal loses electrons to become a positively charged cation, and the nonmetal accepts those electrons to become a negatively charged anion.
isomer
A molecule with the same chemical formula as another molecule, but with a different chemical structure. That is, isomers contain the same number of atoms of each element, but have different arrangements of their atoms.
isotonic solution
Refers to two solutions having the same osmotic pressure across a semipermeable membrane. This state allows for the free movement of water across the membrane without changing the concentration of solutes on either side.
J
jejunum
like gher vertebrates like mammals, birds, and reptiles. It is present between the duodenum and the ileum.
K
kinase
An enzyme that catalyzes the transfer of phosphate groups from high-energy, phosphate-donating molecules to specific substrates.
kingdom
Krebs cycle
See citric acid cycle.
L
larva
(pl.) larvae
A distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development, such as insects, amphibians, or cnidarians, typically have a larval phase of their life cycle.
Law of Independent Assortment
The principle, originally formulated by Gregor Mendel, stating that when two or more characteristics are inherited, individual hereditary factors assort independently during gamete production, giving different traits an equal opportunity of occurring together.
leukocyte
Also called a white blood cell.
A colourless cell of the immune system which circulates in the blood and body fluids and is involved in counteracting foreign substances and disease. There are several types of leukocytes, all amoeboid cells with a nucleus, including lymphocytes, granulocytes, and monocytes.
lichen
life
The characteristic or collection of characteristics that distinguishes physical entities that undergo biological processes (e.g. living organisms) from that those do not (e.g. non-living, inanimate matter), either because such processes have ceased or because they were not present in the first place. What constitutes "life" is notoriously difficult to define, and there is currently no consensus definition, though some popular criteria are that living things are composed of cells, have a life cycle, undergo metabolism, maintain homeostasis, adapt to environments, respond to stimuli, reproduce, and evolve. Biology is the scientific study of life and of living organisms.
life cycle
ligament
The fibrous connective tissue that connects bones to other bones and is also known as articular ligament, articular larua, fibrous ligament, or true ligament.
light-independent reactions
See Calvin cycle.
linked genes
Any set of one or more genes which are sufficiently close together on the same chromosome that they are very unlikely to assort independently and therefore are usually inherited together.
lipid
A substance that is insoluble in water and soluble in alcohol, ether, and chloroform. Lipids are an important component of living cells. Together with carbohydrates and proteins, lipids are the main constituents of plant and animal cells. Cholesterol and triglycerides are lipids.
lipoprotein
A biochemical assembly that contains both proteins and lipids, bound to the proteins, which allow fats to move through the water inside and outside cells. The proteins serve to emulsify the lipid molecules.
M
M phase
Mitosis and cytokinesis together define the mitotic (M) phase of an animal cell cycle – the division of the mother cell into two daughter cells, genetically identical to each other and to their parent cell.
macroevolution
Evolution on a scale of separated gene pools. Macroevolutionary studies focus on change that occurs at or above the level of species, in contrast with microevolution, which refers to smaller evolutionary changes (typically described as changes in allele frequencies) within a species or population.
macromolecule
A very large molecule, such as a protein, commonly created by polymerization of smaller subunits (monomers). They are typically composed of thousands or more atoms.
macronutrient
Nutrients needed in large amounts which provide calories or energy. Nutrients are substances needed for growth, metabolism, and for other body functions. There are three basic types of macronutrients: fats, proteins, and carbohydrates.
macrophage
A kind of swallowing cell, which means it functions by literally swallowing up other particles or smaller cells. Macrophages engulf and digest debris (such as dead cells) and foreign particles through the process of phagocytosis, so macrophages act like scavengers.
mammalogy
The branch of biology that studies mammals, a class of vertebrates with characteristics such as homeothermic metabolism, fur, four-chambered hearts, and complex nervous systems.
marine biology
The study of organisms in the ocean or other marine bodies of water. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies species based on the environment rather than on taxonomy.
mast cell
A cell filled with basophil granules, found in numbers in connective tissue and releasing histamine and other substances during inflammatory and allergic reactions.
mating
medulla
The continuation of the spinal cord within the skull, forming the lowest part of the brainstem and containing control centres for the heart and lungs.
meiosis
A specialized type of cell division in which a dividing parent cell proceeds through two consecutive divisions, ultimately producing four genetically unique daughter cells in each of which the chromosome number is half of that in the original parent cell. This process is exclusive to cells of the sex organs in sexually reproducing eukaryotes, where it serves the purpose of generating gametes such as eggs, sperm, or spores.
membrane potential
When a nerve or muscle cell is at "rest", its membrane potential is called the resting membrane potential. In a typical neuron, this is about –70 millivolts (mV). The minus sign indicates that the inside of the cell is negative with respect to the surrounding extracellular fluid.
messenger RNA
A large family of RNA molecules that convey genetic information from DNA to the ribosome.
metabolism
metamorphosis
metaphase
The third phase of mitosis, in which duplicated genetic material carried in the nucleus of a parent cell is separated into two identical daughter cells. During metaphase, the cell's chromosomes align themselves in the middle of the cell through a type of cellular "tug of war".
microbiology
The study of microscopic organisms, such as bacteria, viruses, archaea, fungi and protozoa. This discipline includes fundamental research on the biochemistry, physiology, cell biology, ecology, evolution and clinical aspects of microorganisms, including the host response to these agents.
microevolution
The alteration in allele frequencies that occurs over time within a population.
mitochondria
(sing.) mitochondrion
mitosis
In eukaryotic cells, the part of the cell cycle during which the division of the nucleus takes place and duplicated chromosomes are separated into two distinct nuclei. Mitosis is generally preceded by the "S" stage of interphase, when the cell's DNA is replicated, and followed by cytokinesis, when the cytoplasm and cell membrane are divided into two new daughter cells. It is similar to but distinct from binary fission and meiosis.
molecule
The smallest particle in a chemical element or compound that has the chemical properties of that element or compound. Molecules are made up of atoms that are held together by chemical bonds. These bonds form as a result of the sharing or exchange of electrons among atoms.
molecular biology
The branch of biology concerning biological activity at the molecular level. The field of molecular biology overlaps with biology and chemistry and in particular with genetics and biochemistry.
molecular switch
A molecule that can be reversibly changed between two or more stable states.
monomer
A molecule that "can undergo polymerization thereby contributing constitutional units to the essential structure of a macromolecule".
morphology
motile
motor neuron
A neuron whose cell body is situated in the motor cortex, brain stem, or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly control effector organs, mainly muscles and glands.
mucous membrane
A membrane that lines various cavities in the body and covers the surface of internal organs.
multicellular
Having or consisting of more than one cell, as opposed to being unicellular.
mycology
The branch of biology concerned with the study of fungi, including their genetic and biochemical properties, their taxonomy and their use to humans as a source for tinder, medicine, food, and entheogens, as well as their dangers, such as poisoning or infection.
myofibril
A basic rod-like unit of a muscle cell.
myosin
A superfamily of motor proteins best known for their roles in muscle contraction and in a wide range of other motility processes in eukaryotes.
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N
natural selection
A process in nature in which organisms possessing certain genotypic characteristics that make them better adjusted to an environment tend to survive, reproduce, increase in number or frequency, and therefore, are able to transmit and perpetuate their essential genotypic qualities to succeeding generations.
neurobiology
Also called neuroscience.
The scientific study of the nervous system.
neuron
An electrically excitable cell that receives, processes, and transmits information through electrical and chemical signals.
neurotransmitter
An endogenous compound that enable neurotransmission.
niche
The role and position an organism or taxon fills within its environment; how it meets its needs for food and shelter, how it survives, and how it reproduces. A species' niche includes all of its interactions with the biotic and abiotic factors of its environment.
nucleic acid
The biopolymers, or small biomolecules, essential to all known forms of life .
nucleic acid sequence
A succession of letters that indicate the order of nucleotides forming alleles within a DNA or RNA molecule.
nucleobase
The nitrogen-containing biological compounds that form nucleosides, which in turn are components of nucleotides, with all of these monomers constituting the basic building blocks of nucleic acids.
nucleoid
An irregularly shaped region within the cell of a prokaryote that contains all or most of the genetic material, called the genophore.
nucleolus
The largest structure within the nucleus of eukaryotic cells.
nucleotide
An organic compound which serves as the fundamental monomer used in the construction of nucleic acid polymers, such as DNA and RNA, both of which are essential biomolecules within all living organisms.
O
offspring
order
organ
A collection of tissues joined in a structural unit to serve a common function.
organism
A contiguous living system.
ornithology
The branch of zoology that concerns the study of birds.
osmosis
The spontaneous net movement of solvent molecules through a semipermeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides.
P
paleontology
The study of the history of life on Earth as reflected in the fossil record. Fossils are the remains or traces of organisms that lived in the geological past and have been preserved in the Earth's crust.
parallel evolution
The development of a similar trait in related, but distinct, species descending from the same ancestor, but from different clades.
parasite
parasitology
The study of parasites, their hosts, and the relationship between them. As a biological discipline, the scope of parasitology is not determined by the organism or environment in question, but by their way of life.
pathobiology
The study or practice of pathology with greater emphasis on the biological than on the medical aspects.
pathogen
In the broadest sense, anything that can produce disease, though the term is most commonly used to refer specifically to an infectious microscopic organism such as a virus, bacterium, protozoan, or another microbial agent which causes disease for a host organism by invading the host's tissues.
pathology
A medical specialty that is concerned with the diagnosis of disease based on the laboratory analysis of bodily fluids such as blood and urine, as well as tissues, using the tools of chemistry, clinical microbiology, hematology, and molecular pathology.
pH
A numeric scale used to specify the acidity or basicity (alkalinity) of an aqueous solution. It is roughly the negative of the logarithm to base 10 of the concentration, measured in units of moles per liter, of hydrogen ions.
pharmacology
The science of drug action on biological systems. In its entirety, it embraces knowledge of the sources, chemical properties, biological effects, and therapeutic uses of drugs.
phenotype
The composite of an organism's observable features or traits, such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior.
pheromone
A secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are analogous to hormones acting outside the body of the secreting individual to impact the behavior of receiving individuals.
phloem
The conducting tissue in plants responsible for the conduction of food particles.
photosynthesis
The process by which nearly all plants and some algae and bacteria convert the energy of sunlight into chemical energy, which is used to synthesize carbohydrates such as sugars from carbon dioxide and water; these carbohydrates are stored as food, and the energy within them is later released to fuel metabolic activities. Organisms that perform photosynthesis are therefore autotrophs. Photosynthesis supplies the majority of the energy necessary for life on Earth.
phylogeny
phylum
A taxonomic rank or level of classification below kingdom and above class; in botany, the term division is commonly used in place of phylum.
physiology
The branch of biology dealing with the functions and activities of living organisms and their parts, including all physical and chemical processes.
phytochemistry
The study of phytochemicals, which are chemicals derived from plants.
phytopathology
The science of diagnosing and managing plant diseases.
placebo
A substance or treatment of no intended therapeutic value.
plant
plasmolysis
The process in which cells lose water in a hypertonic solution.
pollination
The transfer of pollen from a male part of a plant to a female part of a plant, enabling later fertilisation and the production of seeds. Pollen is most commonly transported by animals or by wind.
polymer
A large macromolecule composed of many repeated subunits.
polymerase chain reaction (PCR)
A technique used in molecular biology to amplify a single copy or a few copies of a segment of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence.
polyploidy
Having or containing more than two complete sets of chromosomes.
population
All the organisms of the same group or species that live in a particular geographical area and are capable of interbreeding.
population biology
The study of populations of organisms, especially the regulation of population size, life history traits such as clutch size, and extinction.
population ecology
Also called autoecology.
A subfield of ecology that deals with the dynamics of species populations and how these populations interact with the environment. It is the study of how the population sizes of species change over time and space.
predation
A biological interaction in which a predator kills and eats its prey.
predator
prey
primer
A short strand of RNA or DNA that serves as a starting point for DNA synthesis.
progeny
Any genetic descendant or offspring.
progesterone
An endogenous steroid and progestogen sex hormone which plays a critical role in the menstrual cycle, pregnancy, and embryogenesis in humans and other animal species.
prokaryote
A type of organism which does not have a true nucleus.
protein
A polypeptide chain of amino acids. It is a body-building nutrient.
protist
psychobiology
Also called behavioral neuroscience, biological psychology, and biopsychology.
The application of the principles of biology to the study of physiological, genetic, and developmental mechanisms of behavior in humans and other animals.
R
regeneration
The process of renewal, restoration, and growth that makes genomes, cells, organisms, and ecosystems resilient to natural fluctuations or events that cause disturbance or damage. For example, many organisms are capable of regenerating tissues and even entire body parts if they are lost or destroyed.
reproduction
Also called procreation or breeding.
The biological process by which one or more new individual organisms (known as offspring) is produced from an existing parent organism. Reproduction is a defining characteristic of all life, and every individual organism exists as the result of a reproductive event. There are two general methods by which reproduction takes place: sexual or asexual.
reproductive biology
The branch of biology that studies the various types and mechanisms of reproduction used by living organisms, typically with special emphasis on cell division, fertility, endocrinology, and/or the tissues, organs, and systems involved in reproduction.
ribonucleic acid (RNA)
A nucleic acid polymer composed of a series of ribonucleotides which incorporate a set of four nucleobases: adenine (A), guanine (G), cytosine (C), and uracil (U). Closely related to DNA, RNA molecules serve in a wide variety of essential biological roles, including coding, decoding, regulating, and expressing genes, as well as functioning as signaling molecules.
ribosome
A complex molecular machine, found within all living cells, that serves as the site of biological protein synthesis.
RNA
See ribonucleic acid.
RNA polymerase
A member of a family of enzymes that are essential to life: they are found in all organisms and many viruses.
S
sclerenchyma
A type of tissue in which cells have thick lignified secondary walls and often die when mature.
seed
The embryo, enclosed in a protective outer covering, of certain types of plants.
selective breeding
See artificial selection.
sessile
1. Generally, lacking motility or means of self-locomotion; immobile or incapable of movement. Sessile organisms may move via external forces such as wind or water currents but are more often permanently fixed to a solid object such as a rock, soil, or another organism.
2. In botany, the property of a plant or plant part that is attached directly by its base to an object or another plant part, i.e. without an intervening stem, stalk, or petiole.
sex
sexual reproduction
A type of reproduction in which cells from two parents unite to form the first cell of a new organism.
sociality
The degree to which individuals in an animal population tend to associate in social groups and form cooperative societies.
sociobiology
A branch of biology that is based on the hypothesis that social behavior has resulted from evolution and which attempts to explain and examine social behavior within that context.
soil biology
The study of microbial and faunal activity and ecology in soil.
species
The basic unit of biological classification and the narrowest of the canonical taxonomic ranks, as well as a unit of biodiversity. Species are traditionally distinguished on the basis of reproductive compatibility, though achieving a satisfactory definition that is universally applicable to all life has proven difficult, since many organisms classified as distinct "species" are capable of interbreeding with different (albeit closely related) species, generating hybrids.
speciation
The evolutionary process by which populations of organisms evolve to become distinct species, typically via reproductive isolation.
sperm
spore
stem cell
A type of undifferentiated or partially undifferentiated cell that is capable of differentiating into other types of specialized cells and also capable of dividing to produce more of the same type of stem cell. Stem cells are the earliest type of cell in a cell lineage.
steroid
A biologically active organic compound with four rings arranged in a specific molecular configuration.
strain
A genetic variant, subtype, or culture identified as a distinct taxonomic subdivision within a species. The term is most commonly used to identify particular types of bacteria and viruses.
structural biology
The branch of molecular biology, biochemistry, and biophysics concerned with the molecular structure of biological macromolecules, especially proteins and nucleic acids, how they acquire the structures they have, and how alterations in their structures affect their function.
symbiogenesis
See endosymbiotic theory.
symbiont
Any organism involved in any type of symbiosis with another organism, either of the same or a different species.
symbiosis
Any close and long-term interaction between two different biological organisms, regardless of the nature or degree of the effect on either organism. Examples include mutualism, commensalism, and parasitism.
synthetic biology
An interdisciplinary branch of biology and engineering combining various disciplines from within these domains, including biotechnology, evolutionary biology, molecular biology, systems biology, biophysics, computer engineering, and genetic engineering.
systematics
The scientific study of biodiversity. It is concerned with the discovering and naming of new species of organisms (nomenclature) and arranging these taxa into classification schemes (taxonomy). A large part of modern systematics is concerned with understanding the evolutionary relationships between various taxa (phylogenetics) using methods of comparative biology (e.g. physiology, behavior, biochemistry, morphology, genetics) and statistical analysis.
systems biology
A branch of biology concerned with the computational and mathematical analysis of complex biological systems. It is an interdisciplinary field which combines elements of systems theory and applied mathematics with theoretical biology, with a primary aim to discover and model the emergent properties of interacting biological entities.
T
T cell
A type of lymphocyte that plays a central role in cell-mediated immunity.
taxon
(pl.) taxa
A group of one or more populations of an organism or organisms used by taxonomists to classify organisms into discrete, convenient, and identifiable units.
taxonomy
telophase
testosterone
The primary male sex hormone and an anabolic steroid.
thymine
One of the four nucleobases used in the nucleic acid DNA (but not in RNA). It is represented in DNA sequences by the letter T.
tissue
trait
transcription
The first step of gene expression, in which a particular segment of DNA is copied into RNA by the enzyme RNA polymerase. Both RNA and DNA are nucleic acids, which use complementary base pairs of nucleotides as a common language.
translation
The process by which ribosomes in the cytoplasm or endoplasmic reticulum synthesize proteins following the transcription of DNA to RNA in the cell's nucleus.
trophic level
The position an organism occupies in a food chain.
tumor
Also called a neoplasm.
U
uncoating
The decomposition of a viral capsid. An informal and simplified description of the way a virus infectious material enters the cell, usually appearing in light science material for the general public.
unicellular
Having or consisting of only one cell, as opposed to being multicellular.
uracil
One of the four nucleobases in the nucleic acid of RNA that are represented by the letters A, G, C and U.
urea
An organic compound with chemical formula CO(NH2)2.
urine
A liquid byproduct of metabolism in humans and in many animals.
uterus
A major female hormone-responsive secondary sex organ of the reproductive system in humans and most other mammals.
V
vacuole
A membrane-bound organelle which is present in all plant and fungal cells and some protist, animal, and bacterial cells.
vasodilation
The widening of blood vessels.
vector
vegetative reproduction
Any type of asexual reproduction performed by an organism which is nonetheless capable of sexual reproduction. The term is used primarily for plants.
vertebrate
vesicle
A small structure within or sometimes external to a cell, consisting of fluid enclosed by a lipid bilayer.
vestigiality
The retention during the process of evolution of genetically determined structures or attributes that have lost some or all of their ancestral function in a given species.
virology
The branch of biology that studies viruses.
virus
A submicroscopic, infectious, parasitic particle of genetic material contained in a protein coat and which replicates only inside the living cell of a host organism.
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W
white blood cell
See leukocyte.
whole genome sequencing
The process of determining the complete DNA sequence of a particular organism's entire genome at a single time.
wood
The inner layer of the stems of woody plants such as trees and shrubs, composed of xylem.
X
xanthophyll
A yellow-colored photosynthetic pigment.
xylem
A type of plant tissue responsible for the transport of water from roots to aerial parts of the plant.
Y
yolk
The nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo.
Z
zoology
The branch of biology that studies the animal kingdom, including the structure, embryology, evolution, classification, habits, and geographical distribution of all animals, both living and extinct, and how they interact with their ecosystems.
zooplankton
A type of heterotrophic (sometimes detritivorous) plankton, as opposed to phytoplankton, which instead obtain energy from photosynthesis. Individual zooplankton are usually microscopic, but some (such as jellyfish) are larger and visible to the naked eye.
zygospore
A diploid reproductive stage in the life cycle of many fungi and protists.
zygote
A eukaryotic cell formed by a fertilization event between two gametes.
A
absolute zero
A theoretical condition concerning a system at the lowest limit of the thermodynamic temperature scale, or zero kelvins, at which the system does not emit or absorb energy (i.e. all atoms are at rest). By extrapolating the ideal gas law, the internationally agreed-upon value for absolute zero has been determined as −273.15 °C (−459.67 °F; 0.00 K).
absorbance
absorption
1. The physical or chemical process by which a substance in one state becomes incorporated into and retained by another substance of a different state. Absorption differs from adsorption in that the first substance permeates the entire bulk of the second substance, rather than just adhering to the surface.
2. The process by which matter (typically electrons bound in atoms) takes up the energy of electromagnetic radiation and transforms it into any of various types of internal energy, such as thermal energy. This type of absorption is the principle on which spectrophotometry is based.
abundance
accuracy
How close a measured value is to the actual or true value. Compare precision.
acid
A compound which, when dissolved in water, gives a pH of less than 7.0, or donates a hydrogen ion.
acid anhydride
A compound with two acyl groups bound to a single oxygen atom.
acid dissociation constant (Ka)
Also acid ionization constant or acidity constant.
A quantitative measure of the strength of an acid in solution expressed as an equilibrium constant for a chemical dissociation reaction in the context of acid-base reactions. It is often given as its base-10 cologarithm, pKa.
actinides
Also actinoids.
The periodic series of metallic elements with atomic numbers 89 to 103, from actinium through lawrencium.
activated complex
A structure that forms because of a collision between molecules while new bonds are formed.
activation energy
The minimum energy which must be available to a chemical system with potential reactants in order to result in a chemical reaction.
activity series
See reactivity series.
actual yield
acyclic
Containing only linear structures of atoms (particularly in hydrocarbons).
addition reaction
In organic chemistry, when two or more molecules combine to make a larger one.
adhesion
The tendency of dissimilar particles or surfaces to cling to one another as a result of intermolecular forces. Contrast cohesion.
adsorption
The chemical adhesion of atoms, ions, or molecules of one substance (either a gas, liquid, or dissolved solid) to the surface of another substance, resulting in a film of the first substance being weakly bonded to the interface between the two substances. Adsorption differs from absorption in that it is exclusively a surface phenomenon, while absorption involves entire volumes of materials.
aeration
The mixing of air into a liquid or a solid.
alcohol
Any organic compound consisting of a hydroxyl functional group attached to a saturated carbon atom.
aldehyde
Any organic compound consisting of a carbonyl group attached to a hydrogen atom and any other R-group.
alkali metal
Any of the metallic elements belonging to Group 1 of the periodic table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).
alkaline earth metal
Any of the metallic elements belonging to Group 2 of the periodic table: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
alkane
Any saturated acyclic hydrocarbon.
alkene
An unsaturated hydrocarbon containing at least one pair of double-bonded carbons.
alkyl group
A functional group consisting of an alkane missing a hydrogen atom.
alkyne
An unsaturated hydrocarbon containing at least one pair of triple-bonded carbons.
allomer
A substance that differs in chemical composition but has the same crystalline structure as another substance.
allotrope
Elements that can have different structures (and therefore different forms), such as carbon (diamonds, graphite, and fullerene).
alloy
A mixture of metals or of a metal and another element which in combination exhibit a metallic bonding character. Common examples include bronze, brass, and pewter.
amalgam
Any alloy of mercury with another metal.
amount of substance
Also enplethy, chemical amount, or simply amount.
The number of discrete particles (such as molecules, atoms, ions, electrons, or any other atomic-scale entity) in a given sample of matter, divided by the Avogadro constant. The SI base unit for amount of substance is the mole (mol).
analyte
analytical chemistry
The branch of chemistry which studies and makes use of instruments and methods to separate, quantify, and identify chemical substances, both by classical wet chemistry techniques such as precipitation, extraction, distillation, and observational analysis, and by modern instrumental techniques such as chromatography, spectroscopy, and electrochemistry.
anion
A negatively charged ion. I.e. an atom that has an excess of electrons compared to protons.
anode
1. An electrode through which the conventional electric current (the flow of positive charges) enters into a polarized electrical circuit.
2. The wire or plate of an electrochemical cell having an excess positive charge. Negatively charged anions always move toward the anode. Contrast cathode.
aqueous solution
A solution in which the solvent is water. It is denoted in chemical equations by appending (aq) to a chemical formula.
aromaticity
A chemical property of conjugated rings of atoms, such as benzene, which results in unusually high stability. Such rings are said to be aromatic.
arrow pushing
aryl
Any functional group or substituent derived from an aromatic ring, such as phenyl or naphthyl. The symbol Ar is often used as a placeholder for a generic aryl group in structural diagrams.
atom
A chemical element in its smallest form, made up of protons and neutrons within the nucleus and electrons circling the nucleus.
An atom with protons, neutrons, and electrons labelled
atomic mass
The mass of an atom, typically expressed in unified atomic mass units and nearly equivalent to the mass number.
atomic mass unit
See unified atomic mass unit.
atomic number (Z)
Also proton number.
The number of protons found in the nucleus of an atom of a given chemical element. It is identical to the charge number of the nucleus and is used in the periodic table to uniquely identify each chemical element.
atomic orbital
Any region in which one or more electrons may be found in an individual atom (as opposed to that within a molecule).
atomic radius
atomic weight
average atomic mass
Avogadro's law
Avogadro's number
Also Avogadro constant.
The number of discrete constituent particles (such as molecules, atoms, or ions) in one mole of a substance, defined as exactly 6.02214076×1023 such particles.
azeotrope
A mixture of liquids whose composition is unchanged by distillation.
B
barometer
A device used to measure atmospheric pressure.
base
A substance that accepts a proton and has a pH above 7.0. A common example is sodium hydroxide (NaOH).
base anhydride
Oxides of group I and II metal elements.
beaker
A cylindrical vessel or container with a flat bottom, most commonly a type of glassware, widely used in laboratories for a variety of purposes, such as preparing, holding, containing, collecting, or volumetrically measuring chemicals, samples, or solutions, or as a chamber in which a chemical reaction occurs. Beakers are distinguished from flasks by having straight rather than sloping sides; most beakers also have a small spout in the rim to aid pouring.
Beer–Lambert law
biochemistry
The study of the chemistry of biological systems and organisms.
Bohr model
boiling
See vaporization.
boiling point
Also vaporization point.
The temperature at which a substance changes state from a liquid to a gas (or vapor). It depends on pressure and is usually specified for a given substance under standard conditions.
boiling-point elevation
the process where the boiling point is elevated by adding a substance
bond
Any persistent attraction between atoms, ions, or molecules that enables the formation of chemical compounds. Bonds are created as a result of a wide variety of electrochemical forces, whose strengths can vary considerably; they are broken when these forces are overcome by other forces. The types, strengths, and quantities of bonds holding together chemical substances dictate the structure and bulk properties of matter.
Boyle's law
For a given mass of gas at constant temperature, the volume varies inversely with the pressure.
Bragg's law
Brownian motion
Brønsted–Lowry acid
Any chemical species that readily donates a proton.
Brønsted–Lowry acid–base reaction
Brønsted–Lowry base
Any chemical species that readily accepts a proton.
Büchner flask
buffered solution
Also simply called a buffer.
An aqueous solution consisting of a weak acid and its conjugate base or a weak base and its conjugate acid that resists changes in pH when strong acids or bases are added.
bumping
A phenomenon in which a homogeneous liquid raised to its boiling point becomes superheated and, upon nucleation, rapidly boils to the gas phase, resulting in a violent expulsion of the liquid from the container; in extreme cases, the container itself may shatter. Frequent stirring, the use of an appropriate container, and the use of boiling chips can help prevent bumping.
bung
burette
Also spelled buret.
Glassware used to dispense specific amounts of liquid when precision is necessary (e.g. during titrations and resource-dependent reactions).
C
calorimeter
A device used to measure heat.
carbanion
carbocation
catalyst
Any element or compound that facilitates an increase in the speed of a chemical reaction but which is not consumed or destroyed during the reaction. It is considered both a reactant and a product of the reaction.
cathode
An electrode from which the conventional electric current (the flow of positive charges) exits a polarized electrical circuit. Positively charged cations always move toward the cathode, though the cathode's polarity can be positive or negative depending on the type of electrical device and how it is being operated. Contrast anode.
cation
A positively charged ion.
centrifugation
A laboratory technique which involves the application of centrifugal force to separate particles from a solution according to their size, shape, and density. Larger and/or denser substances migrate away from the axis of a centrifuge, while smaller and/or less dense substances migrate towards the axis.
centrifuge
A device used to separate substances based on size, shape, and density by centrifugation, or the rotation of vessels containing the substances around a centred axis at extremely high velocities.
cell potential
The force in a galvanic cell that pulls electrons through a reducing agent to an oxidizing agent.
chain reaction
charge number
A quantized value of electric charge calculated as the electric charge in coulombs divided by the elementary-charge constant, or z = q/e. Charge numbers for ions are denoted in superscript (e.g. Na+ indicates a sodium ion with a charge number of positive one). Atomic numbers are charge numbers of atomic nuclei.
Charles's law
When the pressure on a sample of a dry gas is held constant, the Kelvin temperature is directly proportional to its volume.
chelating agent
chelation
A type of bonding involving the formation of two separate coordinate covalent bonds between a polydentate ligand and a single central metal ion. The ligand is usually an organic compound called a chelant or chelating agent.
chemical composition
The identity and relative number of the elements that make up a chemical compound, which can often be expressed with a chemical formula.
chemical decomposition
The breakdown of a single particle or entity (such as a molecule or reactive intermediate) into two or more fragments, or a chemical reaction in which two or more products are formed from a single reactant. Contrast chemical synthesis.
chemical formula
Any of various means of concisely displaying information about the chemical composition of a compound or molecule using letters, numbers, and/or typographical symbols. Chemical formulas, such as empirical and molecular formulas, can only indicate the identities and numerical proportions of the atoms in a compound and are therefore more limited in descriptive power than chemical names and structural formulas.
chemical law
A law of nature relevant to chemistry, such as the law of conservation of mass.
chemical nomenclature
chemical process
1. Any method or means of changing one or more chemicals or chemical compounds in any way, either naturally or artificially, spontaneously or by the actions of external forces.
2. In chemical engineering, any method used on an industrial scale (especially in manufacturing) to change the composition of one or more chemicals or materials.
chemical reaction
The change of one or more substances into one or more different substances.
chemical species
Also simply called a chemical.
A chemical substance or ensemble of substances composed of chemically identical molecular entities which can explore the same set of molecular energy levels on a characteristic or delineated time scale.
chemical substance
Also pure substance or simply substance.
A form of matter that has constant chemical composition and characteristic properties and which cannot be separated into simpler components by purely physical methods (i.e. without breaking chemical bonds). It is often called a pure substance to distinguish it from a mixture.
chemical synthesis
The artificial execution of one or more chemical reactions in order to obtain one or more products. In modern laboratory contexts, specific chemical syntheses are both reliable and reproducible.
chemistry
The scientific discipline that studies chemical substances, compounds, and molecules composed of atoms of various chemical elements, as well as their compositions, structures, properties, behaviors, and the changes they undergo during reactions with other substances.
chirality
chromatography
cis–trans isomerism
closed system
cluster
cohesion
The tendency of similar particles or surfaces to cling to one another as a result of intermolecular forces. Contrast adhesion.
colligative property
Any property of a solution that depends upon the ratio of the number of solute particles to the number of solvent particles in the solution, and not on the nature of the chemical species present.
colloid
A mixture of evenly dispersed substances, such as many milks.
combustion
An exothermic reaction between an oxidant and a fuel that produces large amounts of heat and often light.
An example of combustion
Commission on Isotopic Abundances and Atomic Weights (CIAAW)
compression
An area in a longitudinal wave where the particles are closer and pushed in.
compound
A substance that is made up of two or more chemically bonded elements.
concentration
The abundance of a constituent of a mixture divided by the total volume of the mixture. Several different definitions of concentration are widely used in chemistry, including mass concentration, volume concentration, and molar concentration.
condensation
The phase transition of a substance from a gas to a liquid.
condosity
A comparative measurement of the electrical conductivity of a solution defined as the molar concentration of a sodium chloride (NaCl) solution that has the same specific electrical conductance as the solution under test. It is typically expressed in units of moles per litre (or per some other unit of volume).
conductor
Any object or material that allows the flow of an electric current in one or more directions. Contrast insulator.
conformation
The spatial arrangement of atoms affording distinction between stereoisomers which can be interconverted by rotations about formally single bonds.
conjugate acid
conjugate base
conjugated system
cooling curve
coordinate chemistry
coordinate covalent bond
coordination complex
corrosion
An irreversible interfacial chemical reaction of a material with its environment which results in consumption of the material or dissolution into the material of an external component of the environment.
coulomb
The SI unit of electric charge (symbol: C), defined as the charge transported by a constant current of one ampere in one second.
covalent bond
Also molecular bond.
A bond that involves the sharing of electron pairs between atoms. The stable balance of attractive and repulsive forces that occurs between atoms when they share electrons is known as covalent bonding.
The diatomic hydrogen molecule, H2 (right), is formed by a covalent bond when two single hydrogen atoms share two electrons
critical point
The end point of a phase equilibrium curve or pressure-temperature curve at which conditions are such that phase boundaries vanish and a substance's different phases, such as liquid and vapor, can coexist. The critical point is defined by the intersection of a critical temperature, Tc, and a critical pressure, pc; above this temperature and pressure, all distinction between phases disappears and the substance becomes a supercritical fluid.
crystal
A solid whose constituent particles (such as atoms, ions, or molecules) are arranged in an orderly periodic microscopic structure, forming a lattice that extends in all directions. Such materials are often described as crystalline.
crystallography
The branch of chemistry concerned with determining the arrangement of atoms within crystalline solids.
cuvette
A type of glassware used in spectroscopic experiments. It is usually made of plastic, glass, or quartz and should be as clean and clear as possible.
D
d-block
Dalton's law of partial pressures
deionization
The removal of ions, and in water's case, mineral ions such as sodium, iron, and calcium.
deliquescence
A substance's affinity for water, often characterized as its tendency to absorb moisture from the atmosphere to form aqueous solutions. Most strongly deliquescent substances are salts, such as calcium chloride and potassium carbonate.
delocalized electron
Any electron in a molecule, ion, or solid metal that is not associated with an individual atom or covalent bond. The term may refer to electrons involved in resonance in conjugated systems or aromatic compounds; to free electrons which facilitate electrical conductivity; or to electrons within delocalized molecular orbitals encompassing several adjacent atoms.
density
An intensive property of a substance defined as mass per unit volume and expressed by the equation d = m/V.
denticity
The number of donor groups in a single ligand that bind to a central atom in a coordination complex.
dependent variable
deposition
The settling of particles within a solution or mixture.
Dewar flask
See vacuum flask.
diatomic
Composed of two atoms, of the same or different elements. Contrast monatomic and polyatomic.
diatomic molecule
Any molecule composed of only two atoms, of the same or different elements.
diffusion
The net movement of atoms or molecules from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in chemical potential of the diffusing species and depends on the random walk of particles; hence it results in mixing or mass transport without required directed bulk motion.
dimer
An oligomer consisting of two monomers joined by chemical bonds that may variably be strong or weak, covalent or intermolecular. A homodimer consists of two identical molecules; a heterodimer consists of two different molecules.
dipolar bond
dipole
The electric or magnetic separation of charge.
dipole moment
The polarity of a polar covalent bond.
dispersion
A system in which particles of one material are distributed within a continuous phase of another material; the two phases may be in the same or different states of matter. Dispersions of particles sufficiently large for sedimentation are called suspensions, while those of smaller particles are called colloids or solutions.
dissociation
dissolution
Also solvation.
The interaction of a solvent with the molecules or ions of a solute, involving bond formation, hydrogen bonding, and van der Waals forces.
A sodium ion (Na+) forms a solvation complex with water molecules when dissolved in an aqueous solution
distillation
The process of separating the component substances of a liquid mixture by exploiting differences in the relative volatility of the mixture's components through selective boiling and subsequent condensation. The apparatus used to distill a substance is called a still, and the re-condensed substance yielded by the process is called the distillate.
double bond
A bond involving the covalent sharing of two pairs of electrons.
double-replacement reaction
ductility
Also malleability.
A measure of a material's ability to undergo significant plastic deformation before rupturing, typically expressed as percent elongation or percent area reduction from a tensile test and popularly characterized by the material's ability to be stretched into a wire.
E
earth metal
See alkaline earth metal.
electric charge
A measured property (coulombs) that determines electromagnetic interaction.
electrolyte
A solution that conducts a certain amount of electric current and can be split categorically into weak and strong electrolytes.
electrochemical cell
Using a chemical reaction's current, electromotive force is made.
electromagnetic radiation
A type of wave that can go through vacuums as well as material and is classified as a self-propagating wave.
electromagnetic spectrum
electromagnetism
Fields with an electric charge and electrical properties that change the way that particles move and interact.
electromotive force (emf)
electron
A type of subatomic particle with a net charge that is negative.
electron configuration
The distribution of the electrons of an atom or molecule within atomic or molecular orbitals. An extensive system of notation is used to concisely and uniquely display information about the electron configuration of each atomic species. Knowledge of the specific arrangements of electrons in different atoms is useful for understanding chemical bonds and the organization of the periodic table of the elements.
electron deficiency
electron pair
Two electrons which occupy the same molecular orbital but have opposite spins. Electron pairs form chemical bonds or occur as lone pairs of valence electrons; it is also possible for electrons to occur individually as unpaired electrons.
electron shell
An orbital around the nucleus of an atom which contains a fixed number of electrons (usually two or eight).
electronegativity (χ)
A chemical property that describes the tendency of an atom to attract a shared pair of electrons (or electron density) towards itself. An atom's electronegativity is affected both by its nuclear charge (which is proportional to the number of protons in its nucleus) and the number and location of the electrons present in its atomic shells (which influences the distance of the nucleus from the valence electrons). The higher an atom or substituent's electronegativity, the more it attracts electrons towards itself. As it is usually calculated, electronegativity is not a property of an atom alone but rather of an atom within a molecule; it therefore varies with an element's chemical environment, though it is generally considered a transferable property.
electrophile
Any atom or molecule which can accept an electron pair. Most electrophiles carry a net positive charge, include an atom carrying a partial positive charge, or include a neutral atom that does not have a complete octet of electrons, and therefore they attract electron-rich regions of other species; an electrophile with vacant orbitals can accept an electron pair donated by a nucleophile, creating a chemical bond between the two species. Because they accept electrons, electrophiles are Lewis acids by definition.
electrosynthesis
element
A species of atoms having the same number of protons in their atomic nuclei and hence the same atomic number. Chemical elements constitute all of the ordinary matter in the universe; 118 elements have been identified and are organized by their various chemical properties in the periodic table of the elements.
elementary reaction
Any chemical reaction in which one or more chemical species react directly to form products in a single reaction step and with a single transition state, i.e. without any intermediates. Contrast stepwise reaction.
enantiomer
enantiomorph
endothermic process
energy
A system's ability to do work.
enplethy
See amount of substance.
enthalpy
A measure of the total internal energy of a thermodynamic system, usually symbolized by H.
enthalpy of fusion
entropy
The amount of energy not available for work in a closed thermodynamic system, usually symbolized by S.
environmental chemistry
enzyme
A biological protein catalyst that speeds up a chemical reaction.
empirical formula
Gives the simplest whole-number ratio of the atoms of each element present in a compound.
equilibrium
Universally, it is the condition of a system in which all competing influences are balanced. Chemical equilibrium is the state in which the concentrations of the reactants and products have stopped changing in time.
Eppendorf tube
A generalized and trademarked name used to refer to a microcentrifuge tube.
Erlenmeyer flask
A 500-milliliter Erlenmeyer flask
exothermic process
extensive property
A physical quantity whose value is proportional to the size of the system it describes or to the quantity of matter in the system. Examples include mass, volume, enthalpy, and entropy. Contrast intensive property.
extraction
extrinsic property
F
f-block
freezing
The phase transition of a substance from a liquid to a solid.
Faraday constant
A unit of electric charge widely used in electrochemistry which represents 1 mole of electrons: 6.022 × 1023 electrons. It is equal to approximately 96,500 coulombs (F = 96 485.339 9(24) C/mol).
Faraday's laws of electrolysis
A set of two laws pertaining to electrolysis which hold that: a) the mass of a substance altered at an electrode during electrolysis is directly proportional to the quantity of electricity transferred at that electrode; and b) the mass of an elemental material altered at an electrode is directly proportional to the element's equivalent weight.
Fick's laws of diffusion
filtration
Any physical, biological, or chemical operation that separates large particles (often solid matter) from smaller particles (often a fluid) by passing the mixture through a complex lattice structure through which only particles of a sufficiently small size can pass, called a filter. The fluid and small particles which successfully pass through the filter are called the filtrate.
first-order reaction
flask
A vessel or container, most commonly a type of glassware, widely used in laboratories for a variety of purposes, such as preparing, holding, containing, collecting, or volumetrically measuring chemicals, samples, or solutions, or as a chamber in which a chemical reaction occurs. Flasks come in a number of shapes and sizes but are typically characterized by a wider vessel "body" and one or more narrower tubular sections with an opening at the top.
formal charge (FC)
The electric charge assigned to an atom in a molecule, assuming that all electrons in all bonds are shared equally between atoms, regardless of each atom's relative electronegativity. The formal charge of any atom that is part of a molecule can be calculated by the equation F C = V − N − B 2 {\displaystyle FC=V-N-{\frac {B}{2}}\ } FC=V-N-{\frac {B}{2}}\ , where V {\displaystyle V} V is the number of valence electrons of the neutral atom in its ground state; N {\displaystyle N} N is the number of valence electrons of the atom which are not participating in bonds in the molecule; and B {\displaystyle B} B is the number of electrons shared in bonds with other atoms in the molecule.
fractional distillation
free radical
See radical.
freezing-point depression
freezing point
Also crystallization point.
The temperature at which a substance changes state from a liquid to a solid. Because freezing is the reverse of melting, the freezing point of a substance is identical to its melting point, but by convention only the melting point is referred to as a characteristic property of a substance.
frequency
A measurement of the number of cycles of a given process per unit of time. The SI unit for measuring frequency is the hertz (Hz), with 1 Hz = 1 cycle per second.
functional group
G
galvanic cell
A type of battery made up of electrochemicals with two different metals connected by a salt bridge.
gas
One of the four fundamental states of matter, characterized by high-energy particles which fill their container but have no definite shape or volume.
gas chromatography
A type of chromatography commonly used in analytical chemistry to isolate and analyze chemical compounds that can be vaporized without decomposition. Gas chromatography is often used to test the purity of substances, to identify unknown substances, and to measure the relative amounts of the different components of mixtures.
Gay-Lussac's law
A chemical law used for each of the two relationships derived by French chemist Joseph Louis Gay-Lussac and which concern the properties of gases, though the name is more usually applied to his law of combining volumes.
geochemistry
The study of the chemistry and chemical composition of the Earth and geological processes.
Gibbs energy
A value that indicates the spontaneity of a reaction. Usually symbolized as G.
glass
gram-atom
One gram-atom of an element is defined as a collection of 6.023X10^23 atoms.
Grignard reaction
ground glass joint
An apparatus designed to quickly and easily fit two pieces of leak-tight glassware together, featuring ground glass surfaces and typically a custom-made conical taper.
group
Also family.
A vertical column of the periodic table of the elements and the elements that share it. Contrast period.
H
halogen
Any of the five non-metallic elements of Group 17 of the periodic table: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
hadron
A subatomic particle of a type including the baryons and mesons that can take part in the strong interaction.
heat
Energy transferred from one system to another by thermal interaction.
heat of fusion
See enthalpy of fusion.
Henry's law
Hess' law of constant heat summation
Also simply called Hess' law.
A law of physical chemistry which states that the total enthalpy change during the course of a chemical reaction is the same whether the reaction is completed in one step or in multiple steps.
Hund's rules
hydrate
Any substance that contains water or its constituent elements, or any compound formed by the addition of water or its elements to another molecule.
hydration reaction
hydrogen
hydrogen bond
A form of electrostatic interaction between an electronegative atom and a hydrogen atom bound to a second electronegative atom. Hydrogen bonding is unique because the small size of the hydrogen atoms permits proximity of the interacting electrical charges, and may occur as an intermolecular or intramolecular force.
hydrogenation
hydrolysis
The cleavage of a chemical bond by the addition of water.
hygroscopy
I
ideal gas
ideal gas constant
Also universal gas constant.
The proportionality constant in the ideal gas law, defined as 0.08206 L·atm/(K·mol).
ideal gas law
A chemical law which states that the volume of a gas is proportional to the amount of gas and its Kelvin temperature and inversely proportional to its pressure.
ideal solution
A solution for which the gas phase exhibits thermodynamic properties analogous to those of a mixture of ideal gases.
independent variable
indicator
A special compound added to a solution that changes color depending on the acidity of the solution. Different indicators have different colors and are effective within different pH ranges.
induced radioactivity
radioactivity caused by bombarding a stable isotope with elemental particles, forming a radioactive isotope
inert
inorganic compound
Any chemical compound that does not contain carbon, though there are exceptions. Contrast organic compound.
inorganic chemistry
The branch of chemistry concerning the chemical properties and reactions of inorganic compounds. Contrast organic chemistry.
insulator
Any material that resists the flow of an electric current. Contrast conductor.
intensive property
A physical quantity whose value does not depend on the size of the system or the quantity of matter for which it is measured. Examples include density, temperature, and pressure. Contrast extensive property.
intermolecular force
International System of Units (SI)
International Union of Pure and Applied Chemistry (IUPAC)
An international federation of chemists that is recognized as the world authority in developing standards for chemical nomenclature and other methodologies in chemistry.
intramolecular force
intrinsic property
ion
A molecule that has gained or lost one or more electrons from its neutral state and therefore possesses a negative or positive electric charge.
ionic bond
An electrostatic attraction between oppositely charged ions.
An ionic bond between a sodium atom (Na) and a fluorine atom (F). The sodium atom loses its sole valence electron (leaving the atom with a positive electrical charge), and the fluorine atom gains this same electron via an exothermic process (giving the atom a negative electrical charge). The oppositely charged ions are then attracted to each other to form a new compound called sodium fluoride.
ionization
The breaking up of a chemical compound into separate ions.
isoelectronicity
The phenomenon of two or more chemical species (atoms, molecules, ions, etc.) being composed of different elements but having the same number of valence electrons and the same structural arrangement (i.e. the same number of atoms with the same connectivity). Isoelectronic species typically show useful consistency and predictability in their chemical properties.
isomerization
isomers
Ions or molecules with identical chemical formulas but distinct structures or spatial arrangements. Isomers do not necessarily share similar properties. The two main types of isomers are structural isomers and stereoisomers.
isotope
A variant of a particular chemical element which differs in the number of neutrons present in the nucleus. All isotopes of a given element have the same number of protons in each atom.
J
joule (J)
The SI unit of energy (symbol: J). One joule is defined as one Newton-meter.
K
kelvin (K)
The SI base unit of temperature (symbol: K). The Kelvin scale is an absolute thermodynamic temperature scale that uses absolute zero as its null point.
ketone
An organic compound with a carbonyl group between two carbon atoms.
The skeletal formula for a generic ketone, with R and R' denoting variable carbon-containing substituent groups
kinetics
A subfield of chemistry specializing in reaction rates.
kinetic energy
The energy of an object due to its motion.
L
lability
lanthanides
Also lanthanoids.
The periodic series of metallic elements with atomic numbers 57 through 71, from lanthanum through lutetium.
lattice
The unique arrangement of atoms or molecules in a crystalline liquid or solid.
lattice energy
law of conservation of energy
law of conservation of mass
law of multiple proportions
laws of thermodynamics
leveling effect
The effect of a solvent on the chemical properties of acids or bases which are dissolved in the solvent. The strength of a strong acid is limited or "leveled" by the basicity of the solvent, and likewise the strength of a strong base is limited by the acidity of the solvent, such that the effective pH of the solution is higher or lower than might be suggested by the acid's or base's dissociation constant.
Lewis acid
Lewis base
Lewis structure
ligand
An ion, functional group, or other molecule that binds to a central metal atom to form a coordination complex. Such bonding can range from covalent to ionic, but generally involves formal donation of one or more of the ligand's electron pairs to the metal.
light
Also referred to as visible light.
The portion of the electromagnetic spectrum which is visible to the unaided human eye.
liquefaction
liquid
One of the four fundamental states of matter, characterized by nearly incompressible fluid particles that retain a definite volume but no fixed shape.
locant
London dispersion forces
A type of weak intermolecular force.
M
magnetic quantum number
malleability
See ductility.
manometer
An instrument used to measure pressure invented by Evangelista Torricelli in 1643.
mass
A property of physical matter that is a measure of its resistance to acceleration when a net force is applied. The SI base unit for mass is the kilogram (kg).
mass concentration
mass fraction
mass number (A)
Also atomic mass number or nucleon number.
The total number of protons and neutrons (together known as nucleons) within the nucleus of an atom. It determines the atomic mass of the atom. Mass number varies between different isotopes of the same chemical element, and is often included either after the element's name (as in carbon-12) or as a superscript to the left of the element's symbol (as in 12C) to identify a specific isotope.
mass spectrometry (MS)
An analytical technique that measures the mass-to-charge ratio of ions in a chemical sample by bombarding the sample with electrons to the point of ionization and then separating the charged fragments by subjecting them to an electric or magnetic field, typically in order to determine the elemental or isotopic signatures of an unknown substance, the masses of its constituent particles, and/or the identities or structures of the molecules within it. The results are presented as a mass spectrum, a plot of the intensity of ion signals as a function of the mass-to-charge ratio.
matter
Any substance that has mass and takes up space by having volume.
metal
Any chemical element which is a good conductor of both electricity and heat and which readily forms cations and ionic bonds with non-metals.
melting
The phase transition of a substance from a solid to a liquid.
melting point
Also liquefaction point.
The temperature at which a substance changes state from a solid to a liquid. It depends on pressure and is usually specified for a given substance under standard conditions. The melting point of a substance is identical to its freezing point.
metalloid
A chemical element or substance possessing properties of both metals and non-metals.
methylene blue
A heterocyclic aromatic compound with the molecular formula C16H18N3SCl.
microcentrifuge tube
A small plastic, sealable container that is used to store small volumes of liquid, generally less than 2 milliliters.
A 1.7-milliliter microcentrifuge tube or Eppendorf tube containing Coomassie Blue solution
mineral
miscibility
mixture
A material made up of two or more different substances which are mixed physically but are not combined chemically (i.e. a chemical reaction has not taken place which has changed the molecules of the substances into new substances).
moiety
Any named characteristic group, branch, or other part of a large molecule that may be identified within other kinds of molecules as well. Functional groups are typically smaller and more generic than moieties, whereas substituents and side chains may often be classified as moieties and vice versa.
molality
Also molal concentration.
A measure of the concentration of a solute in a solution in terms of the amount of the solute per unit mass of the solvent. Molality is typically expressed in units of moles per kilogram (mol/kg); a solution with a concentration of exactly 1 mol/kg is sometimes said to be 1 molal. Contrast molarity.
molar attenuation coefficient
molar concentration
Also molarity, amount concentration, or substance concentration.
A measure of the concentration of a chemical species, especially of a solute in a solution, in terms of the amount of the species per unit volume of solution. Molarity is typically expressed in units of moles per litre (mol/L); a solution with a concentration of exactly 1 mol/L is commonly said to be 1 molar, symbolized as 1 M. Contrast molality.
molar fraction
Also mole fraction.
molar mass
mole (mol)
A unit (symbol: mol) that measures the amount of a substance in terms of the absolute number of particles or entities composing the substance. A single mole contains approximately 6.022×1023 particles or entities.
molecular formula
molecular orbital (MO)
Any region in which one or more electrons may be found in a molecule (as opposed to that within an individual atom).
molecular orbital diagram
molecule
A number of atoms that are chemically bonded together and collectively electrically neutral.
monatomic
Having only one atom, as opposed to a molecule composed of more than one. Virtually all elements are monatomic in the gas phase at sufficiently high temperatures. Contrast diatomic and polyatomic.
N
natural abundance
neat
Conditions with a liquid reagent or gas performed with no added solvent or cosolvent.
neutron
A type of subatomic particle that is electrically neutral, having no net charge.
nitrogen
nucleon
Either a proton or a neutron, considered in its role as a component of an atomic nucleus.
nucleophile
Any atom or molecule which can donate an electron pair to another atom or molecule. All molecules or ions with a free pair of electrons or at least one pi bond can act as nucleophiles, by which they are attracted to electron-deficient regions of other species; a chemical reaction involving a nucleophile donating an electron pair to an electrophile may be referred to as nucleophilic attack. Because they donate electrons, nucleophiles are Lewis bases by definition.
nucleus
The centre of an atom, made up of neutrons and protons and possessing a net positive electric charge.
noble gas
Also inert gas.
Any of the six non-metallic elements of Group 18 of the periodic table: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). All of the noble gases have outer electron shells that are completely filled in their naturally occurring states, giving them very low chemical reactivity.
non-metal
Any chemical element which is not a metal.
normality
nuclear
Of or pertaining to the atomic nucleus.
nuclear chemistry
The branch of chemistry that studies the various processes and properties relevant to atomic nuclei, including radioactivity.
nuclear magnetic resonance spectroscopy
A technique that exploits the magnetic properties of certain nuclei, useful for identifying unknown compounds. Nuclear magnetic resonance is often abbreviated NMR.
nuclear transmutation
nuclide
A species of atom characterized by its mass number, atomic number, and nuclear energy state, provided that the mean life in that state is long enough to be observable.
number density
A measure of the concentration of countable objects (atoms, molecules, etc.) in space, expressed as the number per unit volume.
O
octet rule
Also Lewis octet rule.
A classical rule for describing the electron configuration of atoms in certain molecules: the maximum number of electron pairs that can be accommodated in the valence shell of an element in the first row of the periodic table is four (or eight total electrons). For elements in the second and subsequent rows, there are many exceptions to this rule.
olefin
A trivial (non-IUPAC) name for any alkene.
optical activity
orbital
Any region of an atom or molecule in which one or more electrons can be found. The term may refer to either an atomic orbital or a molecular orbital.
orbital hybridisation
order of reaction
organic acid
Any organic compound with acidic properties. Contrast organic base.
organic base
Any organic compound with basic properties. Contrast organic acid.
organic compound
Any chemical compound that contains one or more carbon atoms. Contrast inorganic compound.
organic chemistry
The branch of chemistry concerned with the chemical properties and reactions of organic compounds. Contrast inorganic chemistry.
organic redox reaction
osmotic pressure
other metal
Any of the metallic elements in the p-block, which are characterized by having a combination of relatively low melting points (all less than 950 K) and relatively high electronegativity values (all more than 1.6, revised Pauling).
oxidation
oxidation state
Also oxidation number.
1. The degree of oxidation of an individual atom in a chemical compound, measured as the decrease in the number of electrons relative to the atom's naturally occurring elemental state.
2. The hypothetical electric charge (positive, negative, or zero) that an atom would have if all bonds to atoms of different elements were 100% ionic, with no covalent component.
oxidizing agent
oxoacid
Also oxyacid or oxacid.
1. Any acid having oxygen in the acidic group.
2. Any compound which contains oxygen, at least one other element, and at least one hydrogen atom bound to oxygen, and which produces a conjugate base by the loss of positive hydrogen ions.
oxygen
P
p-block
paraffin
1. A trivial (non-IUPAC) name for any alkane.
2. Another name for kerosene.
partial pressure
pascal (Pa)
passivation
pH
A logarithmic scale used to specify the acidity or basicity of an aqueous solution. The pH scale approximates the negative of the base-10 logarithm of the molar concentration of hydrogen ions in a solution. At room temperature, pure water is neutral (pH = 7); solutions with a pH less than 7 are acidic and those with a pH greater than 7 are basic.
phase
A region of space throughout which all physical properties of a substance are essentially uniform, or a region of material that is chemically uniform, physically distinct, and often mechanically separable. The term phase may have several different uses in chemistry contexts; colloquially, it is often used interchangeably with state of matter, but many distinct phases may exist within a single state of matter.
phase transition
1. A transformation of a chemical substance between solid, liquid, and gaseous states of matter and, in rare cases, plasma.
2. The measurable values of the external conditions at which such a transformation occurs.
This diagram shows the nomenclature commonly used for each of the different phase transitions
phi bond
physical chemistry
The branch of chemistry that studies chemical systems in terms of the principles, practices, and concepts of physics, such as motion, energy, force, time, thermodynamics, chemical equilibrium, and statistical mechanics, among others. In contrast to chemical physics, physical chemistry is predominantly (though not entirely) a macroscopic science that studies the physical and chemical interactions of bulk quantities of matter.
pi bond
pipette
Also spelled pipet.
A laboratory tool commonly used in chemistry, biology, and medicine to transfer and dispense a precisely measured volume of liquid.
plasma
One of the four fundamental states of matter, in which very high-energy particles are partially or fully ionized to the point that they display unique properties and behaviors unlike those of the other three states. Plasma does not exist freely on the Earth's surface under natural conditions.
period
A horizontal row of the periodic table of the elements and the elements that share it. Contrast group.
periodic table of the elements
Also simply called the periodic table.
A tabular arrangement of the chemical elements organized by their atomic number, electron configuration, and other chemical properties, whose adopted structure shows periodic trends and is used by chemists to derive relationships between various elements as well as predict the properties and behaviors of undiscovered or newly synthesized elements. The first periodic table of the elements was published by Russian chemist Dmitri Mendeleev in 1869.
The modern periodic table of the elements. The horizontal rows are called periods and the vertical columns are called groups or families.
polarity
potential energy
The stored energy in a body or in a system due to its position in a force field or due to its configuration.
precipitate
The formation of a solid in a solution or inside another solid during a chemical reaction or by diffusion in a solid.
precision
How close the results of multiple experimental trials or observations are to each other. Compare accuracy.
pressure
The force applied perpendicular to the surface of an object per unit area. The SI unit for pressure is the pascal (Pa), though many other units of pressure are also commonly used in chemistry.
photon
A carrier of electromagnetic radiation of all wavelengths (such as gamma rays and radio waves).
polyatomic
Composed of two or more atoms, of the same or different elements. Contrast monatomic and diatomic.
polyatomic ion
A molecule composed of two or more covalently bonded atoms which collectively bear a net electric charge and therefore act as an ion.
protective group
proton
A subatomic particle with a positive electric charge that is found in the nucleus of an atom. Often denoted with the symbol H+.
protonation
The addition of a proton (H+) to an atom, molecule, or ion.
pure substance
See chemical substance.
pyrolysis
The thermal decomposition of materials at elevated temperatures in an inert atmosphere such as a vacuum gas.
Q
quantum mechanics
The study of how atoms, molecules, subatomic particles, etc. behave and are structured.
quark
An elementary particle and a fundamental constituent of matter.
quantum
pl. quanta
R
racemate
An equimolar mixture of a pair of enantiomers which does not exhibit optical activity. The chemical name or formula of a racemate is distinguished from those of the enantiomers by the prefix (±)- or by the symbols RS and SR.
radiation
Energy released in the form of waves or subatomic particles when there is a change from high-energy to low-energy states.
radical
Also free radical.
Any atom, molecule, or ion that has at least one unpaired valence electron. With few exceptions, such unpaired electrons make radicals highly chemically reactive, and therefore organic radicals are usually short-lived.
radioactive decay
The process of an unstable atomic nucleus losing energy by emitting radiation.
Raoult's law
A law of thermodynamics which states that the partial pressure of each gaseous component of an ideal mixture of liquids is equal to the vapor pressure of the pure component multiplied by its molar fraction in the mixture.
rare-earth metal
rate equation
Also rate law.
reactant
Sometimes used interchangeably with reagent.
Any substance that is consumed in the course of a chemical reaction.
reaction mechanism
The step-by-step sequence of elementary reactions by which a larger chemical reaction or overall change occurs. A complete mechanism must describe and explain which bonds are broken and which are formed (and in what order), as well as all reactants, products, and catalysts involved; the amounts of each; all intermediates, activated complexes, and transition states; and the stereochemistry of each chemical species. Because the detailed processes of a complex reaction are not observable in most cases, a reaction mechanism is often a theoretical conjecture based on thermodynamic feasibility and what little support can be gained from experiment.
reaction rate
The speed at which reactants are converted into products in a chemical reaction.
reaction rate constant
reactive intermediate
Also simply called an intermediate.
reactivity
reactivity series
Also activity series.
An empirical, calculated, and structurally analytical progression of a series of metals, arranged by their general reactivity from highest to lowest and used to summarize information about their reactions with acids and water and the methods used to extract them from ores.
reagent
Also another name for a reactant.
A test substance that is added to a system in order to bring about a chemical reaction, or to see whether a reaction occurs.
redox
reducing agent
reduction potential
resonance
retort
A laboratory apparatus used for the distillation or dry distillation of chemical substances, traditionally consisting of a spherical vessel with a long, downward-pointing neck that conducts the condensed vapors produced by distillation into a separate collection vessel.
round-bottom flask
rust
S
s-block
The collective name for the elements in Groups 1 and 2 of the periodic table (the alkali and alkaline metals), as well as hydrogen and helium.
salt
Any ionic compound composed of one or more anions and one or more cations.
salt bridge
A device used to connect reduction with oxidation half-cells in an electrochemical cell.
saline solution
A common term for a solution of sodium chloride (NaCl) dissolved in water (H2O).
Schrödinger equation
A quantum state equation which represents the behaviour of an electron around an atom.
second-order reaction
semiconductor
An electrically conductive solid whose degree of conductivity lies somewhere between that of a conductor and that of an insulator.
serial dilution
side chain
A chemical substituent group that is attached to the core part or "backbone" of a larger molecule, especially an oligomeric or polymeric hydrocarbon chain that branches off of the longer primary chain of a macromolecule, as used in biochemistry and organic chemistry.
single bond
A bond that involves the sharing of one pair of electrons.
skeletal formula
sol
A suspension of solid particles in a liquid. Artificial examples include sol-gels.
solid
One of the four fundamental states of matter, characterized by relatively low-energy particles packed closely together in rigid structures with definite shape and volume. See Young's modulus.
solubility
The property of a solid, liquid, or gaseous solute to dissolve in a solid, liquid, or gaseous solvent. It is typically expressed as the proportion of solute dissolved in the solvent in a saturated solution.
solute
The part of a solution that is dissolved into the solvent. For example, sodium chloride (NaCl) is the solute in a solution of saline water.
solution
A homogeneous mixture made up of multiple substances generally referred to as solutes and solvents.
solvated electron
solvation
See dissolution.
solvation shell
solvent
The part of a solution that dissolves the solute. For example, water (H2O) is the solvent in a solution of saline water.
spectrochemistry
spectrometry
See mass spectrometry.
spectroscopy
The study of radiation and matter, such as X-ray absorption and emission spectroscopy.
standard solution
standard conditions of temperature and pressure (STP)
A standardisation of ambient temperature and pressure used in order to easily compare experimental results. Standard temperature is 25 degrees Celsius (°C) and standard pressure is 100.000 kilopascals (kPa). Standard conditions are often denoted with the abbreviation STP or SATP.
state of matter
The condition of matter existing in a distinct, homogeneous, macroscopic form. Solid, liquid, gas, and plasma are the four traditional states of matter and the most well-known. See also phase.
stepwise reaction
stereochemistry
stereoisomer
Also spatial isomer.
An isomer which possesses an identical chemical composition but which differs in the spatial arrangement of its atoms.
stoichiometry
The calculation of quantities of reactants and products in chemical reactions. Stoichiometry is based on the law of conservation of mass and the observation that quantities of reactants and products typically exist in ratios of positive integers, implying that if the amounts of the separate reactants are known, then the amounts of the products can be calculated.
strong acid
strong base
structural formula
structural isomer
Also constitutional isomer.
subatomic particle
Any particle that is smaller than an atom. Examples include protons, neutrons, and electrons.
sublimation
The phase transition of a substance from a solid to a limewater fuel or gas without an apparent intervening transition to a liquid in the process.
substance
See chemical substance.
substituent
suspension
A heterogeneous mixture that contains solid particles which are sufficiently large for sedimentation to occur, by which such particles separate from and settle out of the fluid over time if left undisturbed. In a suspension, the solute does not dissolve but remains dispersed or suspended throughout the fluid solvent only transiently and with mechanical agitation. Contrast colloid and solution.
T
tarnish
temperature
A proportional measure of the average kinetic energy of the random motions of the constituent microscopic particles of a system. The SI base unit for temperature is the kelvin.
theoretical yield
See yield.
thermal conductivity
The property of a material that allows it to conduct thermal energy or heat (a quantity often denoted by k {\displaystyle k} k).
thermochemistry
The study of the absorption or release of heat during a chemical reaction.
thermodynamics
The study of the effects of changing temperature, volume or pressure (or work, heat, and energy) on a macroscopic scale.
thermodynamic stability
The condition of a system being in its lowest energy state with its environment (equilibrium).
thermometer
An instrument used to measure temperature.
titration
Also titrimetry or volumetric analysis.
A laboratory method of quantitative chemical analysis that is used to determine the concentration of an identified analyte. The procedure involves preparing a particular reagent as a standard solution of known concentration and volume (called the titrant or titrator) and allowing it to react with a solution of the analyte (called the titrand) to determine the latter's concentration.
torr
A unit for measuring pressure, equivalent to 133.322 Pa or 1.3158×10−3 atm.
transition metal
An element whose atoms naturally occur with incompletely filled "d" sub-shells. These elements are grouped as the so-called d-block elements in the periodic table.
transuranic element
Any element with an atomic number greater than 92 (i.e. occurring after uranium in the periodic table). None of the transuranic elements are stable in natural conditions.
triple bond
A bond that involves the covalent sharing of three pairs of electrons (for example, the diatomic nitrogen molecule, N2, is composed of two nitrogen atoms linked by a triple bond).
triple point
The place where temperature and pressure of three phases are the same. Water has a special phase diagram.
A phase diagram showing the triple point and critical point of a substance
Tyndall effect
The effect of light scattering by colloidal or suspended particles.
U
UN number
A four-digit code used to note hazardous and flammable substances.
uncertainty
The notion that any measurement that involves estimation of any amount cannot be exactly reproducible.
uncertainty principle
Knowing the location of a particle makes the momentum uncertain, while knowing the momentum of a particle makes the location uncertain.
unified atomic mass unit (u)
Also Dalton (Da).
A unit of mass approximately equal to the mass of one proton or neutron. It is sometimes equated with the technically distinct and obsolete atomic mass unit and abbreviated amu.
unit cell
The smallest repeating unit of a crystalline lattice.
unit factor
Statements used in converting between units.
unpaired electron
V
vacuum flask
Also Dewar flask or thermos.
A storage vessel consisting of two flasks or other containers, placed one within the other and joined at the neck, and a space in between that is partially evacuated of air, creating a near-vacuum that significantly reduces the transfer of heat between the vessel's interior and its ambient environment. Vacuum flasks can greatly lengthen the time over which their contents remain warmer or cooler than the ambient environment.
valence electron
Any of the outermost electrons of an atom, which are located in electron shells.
valence bond theory
A theory explaining the chemical bonding within molecules by discussing valencies, the number of chemical bonds formed by an atom.
valency
The combining capacity of an element.
van der Waals force
One of the forces (attraction/repulsion) between molecules.
van 't Hoff factor
The ratio of moles of particles in solution to moles of solute dissolved.
vapor
When a substance is below the critical temperature while in the gas phase.
vapor pressure
Also equilibrium vapor pressure.
The pressure exerted by a vapor which is in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. It is commonly described as the tendency of particles to spontaneously escape from the liquid or solid state into the gaseous state and is used as an indication of a liquid's evaporation rate.
vaporization
Also boiling.
The phase transition of a substance from a liquid to a gas.
viscosity
A measure of the resistance of a liquid to flow.
volatility
A material quality which describes how readily a substance vaporizes. At a given temperature and pressure, a substance with high volatility is more likely to exist as a gas, while a substance with low volatility is more likely to exist as a liquid or solid; equivalently, less volatile substances will more readily condense from a gaseous state than highly volatile ones.
volt (V)
A derived unit of electric potential, electric potential difference, and electromotive force, defined as one joule of work per coulomb.
voltmeter
An instrument that measures electrical cell potential.
volume
The quantity of three-dimensional space enclosed by a closed surface, or the space that a substance (solid, liquid, gas, or plasma) or shape occupies or contains. The SI unit for volume is the cubic metre (m3).
volumetric analysis
See titration.
volumetric flask
W
watch glass
A circular, concave piece of glass commonly used in chemistry laboratories as a working surface for various purposes, such as evaporating liquids, holding solids while they are being weighed, heating small amounts of a substance, or as a cover for a beaker.
water
A polar inorganic compound with the chemical formula H2O that is a tasteless, odorless, and generally colorless liquid at standard temperature and pressure, though it also occurs naturally as a solid and a gas at the Earth's surface. It is the most abundant substance on Earth and therefore an integral component of virtually all chemical and biological systems. Water is often described as the "universal solvent" for its inherent ability to dissolve many substances.
wave function
A mathematical function describing the position of an electron in a three-dimensional space.
weak acid
weak base
wet chemistry
Also bench chemistry or classical chemistry.
A form of analytical chemistry which uses classical laboratory methods such as simple observation and elementary chemical tests to study chemicals and chemical reactions, i.e. without the use of sophisticated instruments or automated or computerized analysis. It is often used in schools to teach the principles of chemistry to students.
work
work-up
The series of manipulations required to isolate and purify the desired product or products of a chemical reaction.
X
X-ray
A form of ionizing, electromagnetic radiation between gamma and UV rays in the electromagnetic spectrum.
X-ray diffraction
a method for establishing structures of crystalline solids using single wavelength X-rays and looking at diffraction pattern.
X-ray photoelectron spectroscopy
A spectroscopic technique used to measure the composition of a material.
Y
yield
The quantifiable amount of product produced during a chemical reaction.
Z
zone melting
A way to remove impurities from an element by melting it and slowly travel down an ingot (cast).
zwitterion
A chemical compound whose net charge is zero and hence is electrically neutral. But there are some positive and negative charges in it, due to the formal charge, owing to the partial charges of its constituent atoms.
zinc
A metallic chemical element with atomic number 30 and symbol Zn.
A
Activities of daily living
The tasks of everyday life. These activities include eating, dressing, getting into or out of a bed or chair, taking a bath or shower, and using the toilet. Instrumental activities of daily living are activities related to independent living and include preparing meals, managing money, shopping, doing housework, and using a telephone. Also called ADL. (NCI)
Adverse drug reaction
In the preapproval clinical experience with a new medicinal product or its new usages, particularly as the therapeutic dose(s) may not be established, all noxious and unintended responses to a medicinal product related to any dose should be considered adverse drug reactions. The phrase "responses to a medicinal product" means that a causal relationship between a medicinal product and an adverse event is at least a reasonable possibility, i.e., the relationship cannot be ruled out. Regarding marketed medicinal products: A response to a drug that is noxious and unintended and that occurs at doses normally used in man for prophylaxis, diagnosis, or therapy of diseases or for modification of physiological function. (ICH E6)
Adverse effect
An unwanted side effect of treatment. (NCI)
Adverse event
An unexpected medical problem that happens during treatment with a drug or other therapy. Adverse events do not have to be caused by the drug or therapy, and they may be mild, moderate, or severe. (NCI)
An AE is any untoward medical occurrence in a patient or clinical investigation subject administered a pharmaceutical product and that does not necessarily have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease temporally associated with the use of a medicinal (investigational) product, whether or not related to the medicinal (investigational) product (see the ICH guidance for Clinical Safety Data Management: Definitions and Standards for Expedited Reporting). (ICH E6)
Adverse reaction
An unwanted effect caused by the administration of drugs. Onset may be sudden or develop over time (NLM)
Advocacy and support groups
Organizations and groups that actively support participants and their families with valuable resources, including self-empowerment and survival tools. (NLM)
Animal model
An animal with a disease either the same as or like a disease in humans. Animal models are used to study the development and progression of diseases and to test new treatments before they are given to humans. (NCI)
Animal study
A laboratory experiment using animals to study the development and progression of diseases. Animal studies also test how safe and effective new treatments are before they are tested in people. (NCI)
Applicable regulatory requirement
Any law(s) and regulation(s) addressing the conduct of clinical trials of investigational products of the jurisdiction where trial is conducted. (ICH E6)
Approval (in relation to institutional review boards (IRBs))
The affirmative decision of the IRB that the clinical trial has been reviewed and may be conducted at the institution site within the constraints set forth by the IRB, the institution, good clinical practice (GCP), and the applicable regulatory requirements. (ICH E6)
Approved drugs
In the U.S., the Food and Drug Administration (FDA) must approve a substance as a drug before it can be marketed. The approval process involves several steps including pre-clinical laboratory and animal studies, clinical trials for safety and efficacy, filing of a New Drug Application by the manufacturer of the drug, FDA review of the application, and FDA approval/rejection of application (NLM)
Arm
Any of the treatment groups in a randomized trial. Most randomized trials have two "arms," but some have three "arms," or even more (NLM)
Audit
A systematic and independent examination of trial-related activities and documents to determine whether the evaluated trial-related activities were conducted, and the data were recorded, analyzed, and accurately reported according to the protocol, sponsor's standard operating procedures (SOPs), good clinical practice (GCP), and the applicable regulatory requirement(s). (ICH E6)
Audit certificate
A declaration of confirmation by the auditor that an audit has taken place. (ICH E6)
Audit report
A written evaluation by the sponsor's auditor of the results of the audit. (ICH E6)
Audit trail
Documentation that allows reconstruction of the course of events. (ICH E6)
B
Baseline
1. Information gathered at the beginning of a study from which variations found in the study are measured. 2. A known value or quantity with which an unknown is compared when measured or assessed. 3. The initial time point in a clinical trial, just before a participant starts to receive the experimental treatment which is being tested. At this reference point, measurable values such as CD4 count are recorded. Safety and efficacy of a drug are often determined by monitoring changes from the baseline values. (NLM)
An initial measurement that is taken at an early time point to represent a beginning condition, and is used for comparison over time to look for changes. For example, the size of a tumor will be measured before treatment (baseline) and then afterwards to see if the treatment had an effect. (NCI)
Bayesian approaches
Approaches to data analysis that provide a posterior probability distribution for some parameter (e.g. treatment effect), derived from the observed data and a prior probability distribution for the parameter. The posterior distribution is then used as the basis for statistical inference. (ICH E9)
Best practice
In medicine, treatment that experts agree is appropriate, accepted, and widely used. Health care providers are obligated to provide patients with the best practice. Also called standard therapy or standard of care. (NCI)
Bias
In a scientific research study or clinical trial, a flaw in the study design or the method of collecting or interpreting information. Biases can lead to incorrect conclusions about what the study or clinical trial showed. (NCI)
When a point of view prevents impartial judgment on issues relating to the subject of that point of view. In clinical studies, bias is controlled by blinding and randomization (NLM)
The systematic tendency of any factors associated with the design, conduct, analysis and evaluation of the results of a clinical trial to make the estimate of a treatment effect deviate from its true value. Bias introduced through deviations in conduct is referred to as 'operational' bias. The other sources of bias listed above are referred to as 'statistical'. (ICH E9)
Bioavailable
The ability of a drug or other substance to be absorbed and used by the body. Orally bioavailable means that a drug or other substance that is taken by mouth can be absorbed and used by the body. (NCI)
Bioinformatics
The science of using computers, databases, and math to organize and analyze large amounts of biological, medical, and health information. Information may come from many sources, including patient statistics, tissue specimens, genetics research, and clinical trials. (NCI)
Biological drug
A substance that is made from a living organism or its products and is used in the prevention, diagnosis, or treatment diseases. Biological drugs include antibodies, interleukins, and vaccines. Also called biologic agent or biological agent. (NCI)
Biometrics
The science of collecting and analyzing biologic or health data using statistical methods. Biometrics may be used to help learn the possible causes of a disease in a certain group of people. Also called biostatistics and biometry. (NCI)
Biometry
The science of collecting and analyzing biologic or health data using statistical methods. Biometry may be used to help learn the possible causes of a disease in a certain group of people. Also called biostatistics and biometrics. (NCI)
Biostatistics
The science of collecting and analyzing biologic or health data using statistical methods. Biostatistics may be used to help learn the possible causes of a disease in a certain group of people. Also called biometry and biometrics. (NCI)
Blind
A randomized trial is "Blind" if the participant is not told which arm of the trial he is on. A clinical trial is "Blind" if participants are unaware on whether they are in the experimental or control arm of the study; also called masked. (NLM)
A procedure in which one or more parties to the trial are kept unaware of the treatment assignment(s). Single blinding usually refers to the subject(s) being unaware, and double blinding usually refers to the subject(s), investigator(s), monitor, and, in some cases, data analyst(s) being unaware of the treatment assignment(s). (ICH E6)
Blind review
The checking and assessment of data during the period of time between trial completion (the last observation on the last subject) and the breaking of the blind, for the purpose of finalising the planned analysis. (ICH E9)
Blinded study
A type of study in which the patients (single-blinded) or the patients and their doctors (double-blinded) do not know which drug or treatment is being given. The opposite of a blinded study is an open label study. (NCI)
C
Case report
A detailed report of the diagnosis, treatment, and follow-up of an individual patient. Case reports also contain some demographic information about the patient (for example, age, gender, ethnic origin). (NCI)
Case report form
A printed, optical, or electronic document designed to record all of the protocol-required information to be reported to the sponsor on each trial subject. (ICH E6)
Case series
A group or series of case reports involving patients who were given similar treatment. Reports of case series usually contain detailed information about the individual patients. This includes demographic information (for example, age, gender, ethnic origin) and information on diagnosis, treatment, response to treatment, and follow-up after treatment. (NCI)
Case-control study
A study that compares two groups of people: those with the disease or condition under study (cases) and a very similar group of people who do not have the disease or condition (controls). Researchers study the medical and lifestyle histories of the people in each group to learn what factors may be associated with the disease or condition. For example, one group may have been exposed to a particular substance that the other was not. Also called a retrospective study. (NCI)
Clinical
Pertaining to or founded on observation and treatment of participants, as distinguished from theoretical or basic science. (NLM)
Clinical investigation
Any experiment that involves a test article and one or more human subjects (21CFR50.3)
Clinical investigator
A medical researcher in charge of carrying out a clinical trial's protocol. (NLM)
Clinical practice guidelines
Guidelines developed to help health care professionals and patients make decisions about screening, prevention, or treatment of a specific health condition. (NCI)
Clinical researcher
A health professional who works directly with patients, or uses data from patients, to do research on health and disease and to develop new treatments. Clinical researchers may also do research on how health care practices affect health and disease. (NCI)
Clinical series
A case series in which the patients receive treatment in a clinic or other medical facility. (NCI)
Clinical study or Clinical trial
A type of research study that tests how well new medical approaches work in people. These studies test new methods of screening, prevention, diagnosis, or treatment of a disease. Also called a clinical trial. (NCI)
A clinical trial is a research study to answer specific questions about vaccines or new therapies or new ways of using known treatments. Clinical trials (also called medical research and research studies) are used to determine whether new drugs or treatments are both safe and effective. Carefully conducted clinical trials are the fastest and safest way to find treatments that work in people. Trials are in four phases: Phase I tests a new drug or treatment in a small group; Phase II expands the study to a larger group of people; Phase III expands the study to an even larger group of people; and Phase IV takes place after the drug or treatment has been licensed and marketed. (NLM)
Any investigation in human subjects intended to discover or verify the clinical, pharmacological, and/or other pharmacodynamic effects of an investigational product(s), and/or to identify any adverse reactions to an investigational product(s), and/or to study absorption, distribution, metabolism, and excretion of an investigational product(s) with the object of ascertaining its safety and/or efficacy. The terms clinical trial and clinical study are synonymous. (ICH E6)
Clinical Trial/Study Report
A written description of a trial/study of any therapeutic, prophylactic, or diagnostic agent conducted in human subjects, in which the clinical and statistical description, presentations, and analyses are fully integrated into a single report. (ICH E6)
Clinician
A health professional who takes care of patients. (NCI)
Cohort (statistics)
A group of individuals who share a common trait, such as birth year. In medicine, a cohort is a group that is part of a clinical trial or study and is observed over a period of time. (NCI)
In epidemiology, a group of individuals with some characteristics in common. (NLM)
Cohort study
A research study that compares a particular outcome in groups of individuals who are alike in many ways but differ by a certain characteristic (for example, female nurses who smoke compared with those who do not smoke). (NCI)
Community-based clinical trial (CBCT)
A clinical trial conducted primarily through primary-care physicians rather than academic research facilities. (NLM)
Comparator
An investigational or marketed product (i.e., active control), or placebo, used as a reference in a clinical trial. (ICH E6)
Compassionate use
A method of providing experimental therapeutics prior to final FDA approval for use in humans. This procedure is used with very sick individuals who have no other treatment options. Often, case-by-case approval must be obtained from the FDA for "compassionate use" of a drug or therapy. (NLM)
Compassionate use trial
A way to provide an investigational therapy to a patient who is not eligible to receive that therapy in a clinical trial, but who has a serious or life-threatening illness for which other treatments are not available. Compassionate use trials allow patients to receive promising but not yet fully studied or approved therapies when no other treatment option exists. Also called expanded access trial. (NCI)
Complementary and alternative therapy
Broad range of healing philosophies, approaches, and therapies that Western (conventional) medicine does not commonly use to promote well-being or treat health conditions. Examples include acupuncture, herbs, etc. Internet Address: http://www.nccih.nih.gov. (NLM)
Compliance
Adherence to all the trial-related requirements, good clinical practice (GCP) requirements, and the applicable regulatory requirements. (ICH E6)
Confidentiality regarding trial participants
Refers to maintaining the confidentiality of trial participants including their personal identity and all personal medical information. The trial participants' consent to the use of records for data verification purposes should be obtained prior to the trial and assurance must be given that confidentiality will be maintained. (NLM)
Prevention of disclosure, to other than authorized individuals, of a sponsor's proprietary information or of a subject's identity. (ICH E6)
Consecutive case series
A clinical study that includes all eligible patients identified by the researchers during the study registration period. The patients are treated in the order in which they are identified. This type of study usually does not have a control group. (NCI)
Content validity
The extent to which a variable (e.g. a rating scale) measures what it is supposed to measure. (ICH E9)
Contract
A written, dated, and signed agreement between two or more involved parties that sets out any arrangements on delegation and distribution of tasks and obligations and, if appropriate, on financial matters. The protocol may serve as the basis of a contract. (ICH E6)
Contract Research Organization
A person or an organization (commercial, academic, or other) contracted by the sponsor to perform one or more of a sponsor's trial-related duties and functions. (ICH E6)
Contraindication
A specific circumstance when the use of certain treatments could be harmful. (NLM)
Control
A control is the nature of the intervention control. (NLM)
Control animal
An animal in a study that does not receive the treatment being tested. Comparing the health of control animals with the health of treated animals allows researchers to evaluate the effects of a treatment more accurately. (NCI)
Control group
In a clinical trial, the group that does not receive the new treatment being studied. This group is compared to the group that receives the new treatment, to see if the new treatment works. (NCI)
The standard by which experimental observations are evaluated. In many clinical trials, one group of patients will be given an experimental drug or treatment, while the control group is given either a standard treatment for the illness or a placebo (NLM)
Controlled clinical trial
A clinical study that includes a comparison (control) group. The comparison group receives a placebo, another treatment, or no treatment at all. (NCI)
An experiment or clinical trial that includes a comparison (control) group. (NCI)
Controlled trials
Control is a standard against which experimental observations may be evaluated. In clinical trials, one group of participants is given an experimental drug, while another group (i.e., the control group) is given either a standard treatment for the disease or a placebo. (NLM)
Coordinating Committee
A committee that a sponsor may organize to coordinate the conduct of a multicenter trial. (ICH E6)
Coordinating Investigator
An investigator assigned the responsibility for the coordination of investigators at different centers participating in a multicenter trial. (ICH E6)
D
Data and Safety Monitoring Board or Independent Data Monitoring Committee
DSMB. An impartial group that oversees a clinical trial and reviews the results to see if they are acceptable. This group determines if the trial should be changed or closed. Also called DSMB. (NCI)
An independent committee, composed of community representatives and clinical research experts, that reviews data while a clinical trial is in progress to ensure that participants are not exposed to undue risk. A DSMB may recommend that a trial be stopped if there are safety concerns or if the trial objectives have been achieved. (NLM)
An independent data monitoring committee that may be established by the sponsor to assess at intervals the progress of a clinical trial, the safety data, and the critical efficacy endpoints, and to recommend to the sponsor whether to continue, modify, or stop a trial. (ICH E6 and ICH E9)
Diagnostic trials
Refers to trials that are conducted to find better tests or procedures for diagnosing a particular disease or condition. Diagnostic trials usually include people who have signs or symptoms of the disease or condition being studied. (NLM)
Direct Access
Permission to examine, analyze, verify, and reproduce any records and reports that are important to evaluation of a clinical trial. Any party (e.g., domestic and foreign regulatory authorities, sponsors, monitors, and auditors) with direct access should take all reasonable precautions within the constraints of the applicable regulatory requirement(s) to maintain the confidentiality of subjects' identities and sponsor's proprietary information. (ICH E6)
Documentation
All records, in any form (including, but not limited to, written, electronic, magnetic, and optical records; and scans, x-rays, and electrocardiograms) that describe or record the methods, conduct, and/or results of a trial, the factors affecting a trial, and the actions taken. (ICH E6)
Dose
The amount of medicine taken, or radiation given, at one time. (NCI)
Dose-dependent
Refers to the effects of treatment with a drug. If the effects change when the dose of the drug is changed, the effects are said to be dose-dependent. (NCI)
Dose-limiting
Describes side effects of a drug or other treatment that are serious enough to prevent an increase in dose or level of that treatment. (NCI)
Dose-ranging study
A clinical trial in which two or more doses of an agent (such as a drug) are tested against each other to determine which dose works best and is least harmful. (NLM)
Dose-rate
The strength of a treatment given over a period of time. (NCI)
Double-blind study
A clinical trial design in which neither the participating individuals nor the study staff knows which participants are receiving the experimental drug and which are receiving a placebo (or another therapy). Double-blind trials are thought to produce objective results, since the expectations of the doctor and the participant about the experimental drug do not affect the outcome; also called double-masked study. (NLM)
A clinical trial in which neither the medical staff nor the person knows which of several possible therapies the person is receiving. (NCI)
Double-dummy
A technique for retaining the blind when administering supplies in a clinical trial, when the two treatments cannot be made identical. Supplies are prepared for Treatment A (active and indistinguishable placebo) and for Treatment B (active and indistinguishable placebo). Subjects then take two sets of treatment; either A (active) and B (placebo), or A (placebo) and B (active). (ICH E9)
Dropout
A subject in a clinical trial who for any reason fails to continue in the trial until the last visit required of him/her by the study protocol. (ICH E9)
Drug
Any substance, other than food, that is used to prevent, diagnose, treat or relieve symptoms of a disease or abnormal condition. Also refers to a substance that alters mood or body function, or that can be habit-forming or addictive, especially a narcotic. (NCI)
Drug–drug interaction
A modification of the effect of a drug when administered with another drug. The effect may be an increase or a decrease in the action of either substance, or it may be an adverse effect that is not normally associated with either drug. (NLM)
E
Efficacy
The maximum ability of a drug or treatment to produce a result regardless of dosage. A drug passes efficacy trials if it is effective at the dose tested and against the illness for which it is prescribed. In the procedure mandated by the FDA, Phase II clinical trials gauge efficacy, and Phase III trials confirm it (NLM)
Effectiveness. In medicine, the ability of an intervention (for example, a drug or surgery) to produce the desired beneficial effect. (NCI)
Eligibility criteria
In clinical trials, requirements that must be met for an individual to be included in a study. These requirements help make sure that patients in a trial are similar to each other in terms of specific factors such as age, general health, and previous treatment. When all participants meet the same eligibility criteria, it gives researchers greater confidence that results of the study are caused by the intervention being tested and not by other factors. (NCI)
Summary criteria for participant selection; includes Inclusion and Exclusion criteria. (NLM)
Empirical
Based on experimental data, not on a theory. (NLM)
Endpoint
In clinical trials, an event or outcome that can be measured objectively to determine whether the intervention being studied is beneficial. The endpoints of a clinical trial are usually included in the study objectives. Some examples of endpoints are survival, improvements in quality of life, relief of symptoms, and disappearance of the tumor. (NCI)
Overall outcome that the protocol is designed to evaluate. Common endpoints are severe toxicity, disease progression, or death. (NLM)
Enrolling
The act of signing up participants into a study. Generally this process involves evaluating a participant with respect to the eligibility criteria of the study and going through the informed consent process. (NLM)
Epidemiology
The branch of medical science that deals with the study of incidence and distribution and control of a disease in a population. (NLM)
The study of the patterns, causes, and control of disease in groups of people. (NCI)
Equivalence trial
A trial with the primary objective of showing that the response to two or more treatments differs by an amount which is clinically unimportant. This is usually demonstrated by showing that the true treatment difference is likely to lie between a lower and an upper equivalence margin of clinically acceptable differences. (ICH E9)
Essential Documents
Documents that individually and collectively permit evaluation of the conduct of a study and the quality of the data produced. (ICH E6)
Evaluable disease
Disease that cannot be measured directly by the size of the tumor but can be evaluated by other methods specific to a particular clinical trial. (NCI)
Evaluable patients
Patients whose response to a treatment can be measured because enough information has been collected. (NCI)
Expanded access
Refers to any of the FDA procedures, such as compassionate use, parallel track, and treatment IND that distribute experimental drugs to participants who are failing on currently available treatments for their condition and also are unable to participate in ongoing clinical trials. (NLM)
Expanded access trial
A way to provide an investigational therapy to a patient who is not eligible to receive that therapy in a clinical trial, but who has a serious or life-threatening illness for which other treatments are not available. Expanded access allows a patient to receive promising but not yet fully studied or approved therapies when no other treatment option exists. Also called compassionate use trial. (NCI)
Experimental
In clinical trials, refers to a drug (including a new drug, dose, combination, or route of administration) or procedure that has undergone basic laboratory testing and received approval from the U.S. Food and Drug Administration (FDA) to be tested in human subjects. A drug or procedure may be approved by the FDA for use in one disease or condition, but be considered experimental in other diseases or conditions. Also called investigational. (NCI)
Experimental drug
A drug that is not FDA licensed for use in humans, or as a treatment for a particular condition (NLM)
A substance that has been tested in a laboratory and has gotten approval from the U.S. Food and Drug Administration (FDA) to be tested in people. A drug may be approved by the FDA for use in one disease or condition but be considered experimental or investigational in other diseases or conditions. Also called investigational drug. (NCI)
F
Follow-up
Monitoring a person's health over time after treatment. This includes keeping track of the health of people who participate in a clinical study or clinical trial for a period of time, both during the study and after the study ends. (NCI)
Food and Drug Administration (FDA)
The U.S. Department of Health and Human Services agency responsible for ensuring the safety and effectiveness of all drugs, biologics, vaccines, and medical devices, including those used in the diagnosis, treatment, and prevention of HIV infection, AIDS, and AIDS-related opportunistic infections. The FDA also works with the blood banking industry to safeguard the nation's blood supply. Internet address: https://www.fda.gov/. (NLM)
Frequentist methods
Statistical methods, such as significance tests and confidence intervals, which can be interpreted in terms of the frequency of certain outcomes occurring in hypothetical repeated realisations of the same experimental situation. (ICH E9)
Full analysis set
The set of subjects that is as close as possible to the ideal implied by the intention-to- treat principle. It is derived from the set of all randomised subjects by minimal and justified elimination of subjects. (ICH E9)
G
Generalisability, Generalisation
The extent to which the findings of a clinical trial can be reliably extrapolated from the subjects who participated in the trial to a broader patient population and a broader range of clinical settings. (ICH E9)
Global assessment variable
A single variable, usually a scale of ordered categorical ratings, which integrates objective variables and the investigator's overall impression about the state or change in state of a subject. (ICH E9)
Good clinical practice
A standard for the design, conduct, performance, monitoring, auditing, recording, analyses, and reporting of clinical trials that provides assurance that the data and reported results are credible and accurate, and that the rights, integrity, and confidentiality of trial subjects are protected. (ICH E6)
H
Healthy control
In a clinical study, a person who does not have the disorder or disease being studied. Results from healthy controls are compared to results from the group being studied. (NCI)
Historic cohort study
A research study in which the medical records of groups of individuals who are alike in many ways but differ by a certain characteristic (for example, female nurses who smoke and those who do not smoke) are compared for a particular outcome. Also called a retrospective cohort study. (NCI)
Historical control subject
An individual treated in the past and used in a comparison group when researchers analyze the results of a clinical study that had no control group. The use of a control, or comparison, group helps researchers determine the effects of a new treatment more accurately. (NCI)
Human subject
An individual who is or becomes a participant in research, either as a recipient of the test article or as a control. A subject may be either a healthy human or a patient. (21CFR50.3)
Hypothesis
A supposition or assumption advanced as a basis for reasoning or argument, or as a guide to experimental investigation. (NLM)
I
Impartial Witness
A person, who is independent of the trial, who cannot be unfairly influenced by people involved with the trial, who attends the informed consent process if the subject or the subject's legally acceptable representative cannot read, and who reads the informed consent form and any other written information supplied to the subject. (ICH E6)
In vitro
In the laboratory (outside the body). The opposite of in vivo (in the body). (NCI)
In vivo
In the body. The opposite of in vitro (outside the body or in the laboratory). (NCI)
Incidence
The number of new cases of a disease diagnosed each year. (NCI)
Inclusion/exclusion criteria
The medical or social standards determining whether a person may or may not be allowed to enter a clinical trial. These criteria are based on such factors as age, gender, the type and stage of a disease, previous treatment history, and other medical conditions. It is important to note that inclusion and exclusion criteria are not used to reject people personally, but rather to identify appropriate participants and keep them safe. (NLM)
Independent Ethics Committee
An independent body (a review board or a committee, institutional, regional, national, or supranational), constituted of medical/scientific professionals and nonmedical/nonscientific members, whose responsibility it is to ensure the protection of the rights, safety, and well-being of human subjects involved in a trial and to provide public assurance of that protection, by, among other things, reviewing and approving/providing favorable opinion on the trial protocol, the suitability of the investigator(s), facilities, and the methods and material to be used in obtaining and documenting informed consent of the trial subjects. The legal status, composition, function, operations, and regulatory requirements pertaining to Independent Ethics Committees may differ among countries, but should allow the Independent Ethics Committee to act in agreement with GCP as described in this guidance. (ICH E6)
Indication
In medicine, a sign, symptom, or medical condition that leads to the recommendation of a treatment, test, or procedure. (NCI)
Informed consent
A process in which a person is given important facts about a medical procedure or treatment, a clinical trial, or genetic testing before deciding whether or not to participate. It also includes informing the patient when there is new information that may affect his or her decision to continue. Informed consent includes information about the possible risks, benefits, and limits of the procedure, treatment, trial, or genetic testing. (NCI)
The process of learning the key facts about a clinical trial before deciding whether or not to participate. It is also a continuing process throughout the study to provide information for participants. To help someone decide whether or not to participate, the doctors and nurses involved in the trial explain the details of the study. (NLM)
A process by which a subject voluntarily confirms his or her willingness to participate in a particular trial, after having been informed of all aspects of the trial that are relevant to the subject's decision to participate. Informed consent is documented by means of a written, signed, and dated informed consent form. (ICH E6)
Informed consent document
A document that describes the rights of the study participants, and includes details about the study, such as its purpose, duration, required procedures, and key contacts. Risks and potential benefits are explained in the informed consent document. The participant then decides whether or not to sign the document. Informed consent is not a contract, and the participant may withdraw from the trial at any time. (NLM)
Inspection
The act by a regulatory authority(ies) of conducting an official review of documents, facilities, records, and any other resources that are deemed by the authority(ies) to be related to the clinical trial and that may be located at the site of the trial, at the sponsor's and/or contract research organization’s (CROs) facilities, or at other establishments deemed appropriate by the regulatory authority(ies). (ICH E6)
Institution
Any public or private entity or agency or medical or dental facility where clinical trials are conducted. (ICH E6)
Any public or private entity or agency (including Federal, State, and other agencies). (21CFR50.3)
Institutional Review Board (IRB)
1. A committee of physicians, statisticians, researchers, community advocates, and others that ensures that a clinical trial is ethical and that the rights of study participants are protected. All clinical trials in the U.S. must be approved by an IRB before they begin. 2. Every institution that conducts or supports biomedical or behavioral research involving human participants must, by federal regulation, have an IRB that initially approves and periodically reviews the research in order to protect the rights of human participants. (NLM)
A group of scientists, doctors, clergy, and consumers that reviews and approves the action plan for every clinical trial. There is an Institutional Review Board at every health care facility that does clinical research. Institutional Review Boards are designed to protect the people who take part in a clinical trial. Institutional Review Boards check to see that the trial is well designed, legal, ethical, does not involve unnecessary risks, and includes safeguards for patients. Also called IRB. (NCI)
An independent body constituted of medical, scientific, and nonscientific members, whose responsibility it is to ensure the protection of the rights, safety, and well-being of human subjects involved in a trial by, among other things, reviewing, approving, and providing continuing review of trials, of protocols and amendments, and of the methods and material to be used in obtaining and documenting informed consent of the trial subjects. (ICH E6)
Any board, committee, or other group formally designated by an institution to review biomedical research involving humans as subjects, to approve the initiation of and conduct periodic review of such research. (21CFR50.3)
Intent to treat
Analysis of clinical trial results that includes all data from participants in the groups to which they were randomized even if they never received the treatment. (NLM)
The principle that asserts that the effect of a treatment policy can be best assessed by evaluating on the basis of the intention to treat a subject (i.e. the planned treatment regimen) rather than the actual treatment given. It has the consequence that subjects allocated to a treatment group should be followed up, assessed and analysed as members of that group irrespective of their compliance to the planned course of treatment. (ICH E9)
Interaction (Qualitative & Quantitative)
The situation in which a treatment contrast (e.g. difference between investigational product and control) is dependent on another factor (e.g. centre). A quantitative interaction refers to the case where the magnitude of the contrast differs at the different levels of the factor, whereas for a qualitative interaction the direction of the contrast differs for at least one level of the factor. (ICH E9)
Inter-rater reliability
The property of yielding equivalent results when used by different raters on different occasions. (ICH E9)
Interim analysis
Any analysis intended to compare treatment arms with respect to efficacy or safety at any time prior to the formal completion of a trial. (ICH E9)
Interim Clinical Trial/Study Report
A report of intermediate results and their evaluation based on analyses performed during the course of a trial. (ICH E6)
Intervention
In medicine, a treatment or action taken to prevent or treat disease, or improve health in other ways. (NCI)
Primary interventions being studied: types of interventions are Drug, Gene Transfer, Vaccine, Behavior, Device, or Procedure. (NLM)
Intervention group
The group receiving the study agent that is being tested in a clinical trial or clinical study. (NCI)
Intervention name
The generic name of the precise intervention being studied. (NLM)
Intra-rater reliability
The property of yielding equivalent results when used by the same rater on different occasions. (ICH E9)
Investigational
In clinical trials, refers to a drug (including a new drug, dose, combination, or route of administration) or procedure that has undergone basic laboratory testing and received approval from the U.S. Food and Drug Administration (FDA) to be tested in human subjects. A drug or procedure may be approved by the FDA for use in one disease or condition, but be considered investigational in other diseases or conditions. Also called experimental. (NCI)
Investigational drug
A substance that has been tested in a laboratory and has gotten approval from the U.S. Food and Drug Administration (FDA) to be tested in people. A drug may be approved by the FDA for use in one disease or condition but be considered investigational in other diseases or conditions. Also called experimental drug. (NCI)
A pharmaceutical form of an active ingredient or placebo being tested or used as a reference in a clinical trial, including a product with a marketing authorization when used or assembled (formulated or packaged) in a way different from the approved form, or when used for an unapproved indication, or when used to gain further information about an approved use. (ICH E6)
Investigational New Drug
A new drug, antibiotic drug, or biological drug that is used in a clinical investigation. It also includes a biological product used in vitro for diagnostic purposes. (NLM)
Investigator
A researcher in a clinical trial or clinical study. (NCI)
A person responsible for the conduct of the clinical trial at a trial site. If a trial is conducted by a team of individuals at a trial site, the investigator is the responsible leader of the team and may be called the principal investigator. (ICH E6)
An individual who actually conducts a clinical investigation, i.e., under whose immediate direction the test article is administered or dispensed to, or used involving, a subject, or, in the event of an investigation conducted by a team of individuals, is the responsible leader of that team. (21CFR50.3)
Investigator's Brochure
A compilation of the clinical and nonclinical data on the investigational product(s) that is relevant to the study of the investigational product(s) in human subjects. (ICH E6)
L
Legally Acceptable Representative
An individual or juridical or other body authorized under applicable law to consent, on behalf of a prospective subject, to the subject's participation in the clinical trial. (ICH E6)
Levels of evidence
A ranking system used to describe the strength of the results measured in a clinical trial or research study. The design of the study (such as a case report for an individual patient or a randomized double-blinded controlled clinical trial) and the endpoints measured (such as survival or quality of life) affect the strength of the evidence. (NCI)
M
Masked
The knowledge of intervention assignment. (NLM)
Maximum tolerated dose
The highest dose of a drug or treatment that does not cause unacceptable side effects. The maximum tolerated dose is determined in clinical trials by testing increasing doses on different groups of people until the highest dose with acceptable side effects is found. Also called MTD. (NCI)
Medication
A legal drug that is used to prevent, treat, or relieve symptoms of a disease or abnormal condition. (NCI)
Medicine
Refers to the practices and procedures used for the prevention, treatment, or relief of symptoms of a diseases or abnormal conditions. This term may also refer to a legal drug used for the same purpose. (NCI)
Meta-analysis
The formal evaluation of the quantitative evidence from two or more trials bearing on the same question. This most commonly involves the statistical combination of summary statistics from the various trials, but the term is sometimes also used to refer to the combination of the raw data. (ICH E9)
Monitoring Report
A written report from the monitor to the sponsor after each site visit and/or other trial-related communication according to the sponsor's SOPs. (ICH E6)
Monitoring
The act of overseeing the progress of a clinical trial, and of ensuring that it is conducted, recorded, and reported in accordance with the protocol, standard operating procedures (SOPs), GCP, and the applicable regulatory requirement(s). (ICH E6)
Multicenter study
A clinical trial that is carried out at more than one medical institution. (NCI)
A clinical trial conducted according to a single protocol but at more than one site, and, therefore, carried out by more than one investigator. (ICH E6 and ICH E9)
Multidisciplinary opinion
A treatment planning approach in which a number of doctors who are experts in different specialties (disciplines) review and discuss the medical condition and treatment options of a patient. (NCI)
Multiplicity
A large number or variety. (NCI)
N
National Institutes of Health
NIH. A federal agency in the U.S. that conducts biomedical research in its own laboratories; supports the research of non-Federal scientists in universities, medical schools, hospitals, and research institutions throughout the country and abroad; helps in the training of research investigators; and fosters communication of medical information. Access the National Institutes of Health Web site at http://www.nih.gov. Also called NIH. (NCI)
Natural history study
A study that follows a group of people over time who have, or are at risk of developing, a specific medical condition or disease. A natural history study collects health information in order to understand how the medical condition or disease develops and how to treat it. (NCI)
Study of the natural development of something (such as an organism or a disease) over a period of time. (NLM)
New Drug Application (NDA)
An application submitted by the manufacturer of a drug to the FDA - after clinical trials have been completed - for a license to market the drug for a specified indication. (NLM)
Nonblinded
Describes a clinical trial or other experiment in which the researchers know what treatments are being given to each study subject or experimental group. If human subjects are involved, they know what treatments they are receiving. (NCI)
Nonclinical Study
Biomedical studies not performed on human subjects. (ICH E6)
Nonconsecutive case series
A clinical study that includes some, but not all, of the eligible patients identified by the researchers during the study registration period. This type of study does not usually have a control group. (NCI)
Non-inferiority trial
A trial with the primary objective of showing that the response to the investigational product is not clinically inferior to a comparative agent (active or placebo control). (ICH E9)
Nonrandomized clinical trial
A clinical trial in which the participants are not assigned by chance to different treatment groups. Participants may choose which group they want to be in, or they may be assigned to the groups by the researchers. (NCI)
O
Objective improvement
An improvement that can be measured by the health care provider (NCI)
Objective response
A measurable response. (NCI)
Observation
Closely monitoring a patient's condition but withholding treatment until symptoms appear or change. Also called watchful waiting, active surveillance, and expectant management. (NCI)
Observational study
A type of study in which individuals are observed or certain outcomes are measured. No attempt is made to affect the outcome (for example, no treatment is given). (NCI)
Off-label
Describes the legal use of a prescription drug to treat a disease or condition for which the drug has not been approved by the U.S. Food and Drug Administration. (NCI)
A drug prescribed for conditions other than those approved by the FDA. (NLM)
Open label study
A type of study in which both the health providers and the patients are aware of the drug or treatment being given. (NCI)
A clinical trial in which doctors and participants know which drug or vaccine is being administered. (NLM)
Orphan drugs
An FDA category that refers to medications used to treat diseases and conditions that occur rarely. There is little financial incentive for the pharmaceutical industry to develop medications for these diseases or conditions. Orphan drug status, however, gives a manufacturer specific financial incentives to develop and provide such medications. (NLM)
Outcome
A specific result or effect that can be measured. Examples of outcomes include decreased pain, reduced tumor size, and improvement of disease. (NCI)
Outpatient
A patient who visits a health care facility for diagnosis or treatment without spending the night. Sometimes called a day patient. (NCI)
Over-the-counter drug
A medicine that can be bought without a prescription (doctor's order). Examples include analgesics (pain relievers) such as aspirin and acetaminophen. Also called nonprescription and OTC. (NCI)
P
Patient advocate
A person who helps a patient work with others who have an effect on the patient's health, including doctors, insurance companies, employers, case managers, and lawyers. A patient advocate helps resolve issues about health care, medical bills, and job discrimination related to a patient's medical condition. (NCI)
Peer review
Review of a clinical trial by experts chosen by the study sponsor. These experts review the trials for scientific merit, participant safety, and ethical considerations. (NLM)
Per protocol set (Valid Cases, Efficacy Sample, Evaluable Subjects Sample)
The set of data generated by the subset of subjects who complied with the protocol sufficiently to ensure that these data would be likely to exhibit the effects of treatment, according to the underlying scientific model. Compliance covers such considerations as exposure to treatment, availability of measurements and absence of major protocol violations. (ICH E9)
Pharmacokinetics
The processes (in a living organism) of absorption, distribution, metabolism, and excretion of a drug or vaccine. (NLM)
Phase I clinical trials
The first step in testing a new treatment in humans. These studies test the best way to give a new treatment (for example, by mouth, intravenous infusion, or injection) and the best dose. The dose is usually increased a little at a time in order to find the highest dose that does not cause harmful side effects. Because little is known about the possible risks and benefits of the treatments being tested, phase I trials usually include only a small number of patients who have not been helped by other treatments. (NCI)
Initial studies to determine the metabolism and pharmacologic actions of drugs in humans, the side effects associated with increasing doses, and to gain early evidence of effectiveness; may include healthy participants and/or patients. (NLM)
Phase 1 includes the initial introduction of an investigational new drug into humans. Phase 1 studies are typically closely monitored and may be conducted in patients or normal volunteer subjects. These studies are designed to determine the metabolism and pharmacologic actions of the drug in humans, the side effects associated with increasing doses, and, if possible, to gain early evidence on effectiveness. During Phase 1, sufficient information about the drug's pharmacokinetics and pharmacological effects should be obtained to permit the design of well-controlled, scientifically valid, Phase 2 studies. The total number of subjects and patients included in Phase 1 studies varies with the drug, but is generally in the range of 20 to 80. Phase 1 studies also include studies of drug metabolism, structure-activity relationships, and mechanism of action in humans, as well as studies in which investigational drugs are used as research tools to explore biological phenomena or disease processes. (21CFR312)
Phase I/II trial
A trial to study the safety, dosage levels, and response to a new treatment. (NCI)
Phase II clinical trials
A study to test whether a new treatment has an effect (NCI)
Controlled clinical studies conducted to evaluate the effectiveness of the drug for a particular indication or indications in patients with the disease or condition under study and to determine the common short-term side effects and risks. (NLM)
Phase 2 includes the controlled clinical studies conducted to evaluate the effectiveness of the drug for a particular indication or indications in patients with the disease or condition under study and to determine the common short-term side effects and risks associated with the drug. Phase 2 studies are typically well controlled, closely monitored, and conducted in a relatively small number of patients, usually involving no more than several hundred subjects. (21CFR312)
Phase II/III trial
A trial to study response to a new treatment and the effectiveness of the treatment compared with the standard treatment regimen. (NCI)
Phase III clinical trials
A study to compare the results of people taking a new treatment with the results of people taking the standard treatment (for example, which group has better survival rates or fewer side effects). In most cases, studies move into phase III only after a treatment seems to work in phases I and II. Phase III trials may include hundreds of people. (NCI)
Expanded controlled and uncontrolled trials after preliminary evidence suggesting effectiveness of the drug has been obtained, and are intended to gather additional information to evaluate the overall benefit-risk relationship of the drug and provide and adequate basis for physician labeling. (NLM)
Phase 3 studies are expanded controlled and uncontrolled trials. They are performed after preliminary evidence suggesting effectiveness of the drug has been obtained, and are intended to gather the additional information about effectiveness and safety that is needed to evaluate the overall benefit-risk relationship of the drug and to provide an adequate basis for physician labeling. Phase 3 studies usually include from several hundred to several thousand subjects. (21CFR312)
Phase IV clinical trial
After a treatment has been approved and is being marketed, it is studied in a phase IV trial to evaluate side effects that were not apparent in the phase III trial. Thousands of people are involved in a phase IV trial. (NCI)
Post-marketing studies to delineate additional information including the drug's risks, benefits, and optimal use. (NLM)
Pilot study
The initial study examining a new method or treatment. (NCI)
Placebo
A placebo is an inactive pill, liquid, or powder that has no treatment value. In clinical trials, experimental treatments are often compared with placebos to assess the treatment's effectiveness. (NLM)
An inactive substance or treatment that looks the same as, and is given the same way as, an active drug or treatment being tested. The effects of the active drug or treatment are compared to the effects of the placebo. (NCI)
Placebo controlled study
A method of investigation of drugs in which an inactive substance (the placebo) is given to one group of participants, while the drug being tested is given to another group. The results obtained in the two groups are then compared to see if the investigational treatment is more effective in treating the condition. (NLM)
Refers to a clinical study in which the control patients receive a placebo. (NCI)
Placebo effect
A physical or emotional change, occurring after a substance is taken or administered, that is not the result of any special property of the substance. The change may be beneficial, reflecting the expectations of the participant and, often, the expectations of the person giving the substance. (NLM)
Placebo therapy
An inactive treatment or procedure that is intended to mimic as closely as possible a therapy in a clinical trial. Also called sham therapy. (NCI) The term also refers to psychotherapy that obtains its positive effect through the use of principles of social influence.[citation needed]
Population study
A study of a group of individuals taken from the general population who share a common characteristic, such as age, sex, or health condition. This group may be studied for different reasons, such as their response to a drug or risk of getting a disease. (NCI)
Preclinical
Refers to the testing of experimental drugs in the test tube or in animals - the testing that occurs before trials in humans may be carried out. (NLM)
Research using animals to find out if a drug, procedure, or treatment is likely to be useful. Preclinical studies take place before any testing in humans is done. (NCI)
Predictive factor
A situation or condition that may increase a person's risk of developing a certain disease or disorder. (NCI)
Prevention
In medicine, action taken to decrease the chance of getting a disease or condition. (NCI)
Prevention trials
Refers to trials to find better ways to prevent disease in people who have never had the disease or to prevent a disease from returning. These approaches may include medicines, vaccines, vitamins, minerals, or lifestyle changes. (NLM)
Preventive
Used to prevent disease. (NCI)
Primary endpoint
The main result that is measured at the end of a study to see if a given treatment worked (e.g., the number of deaths or the difference in survival between the treatment group and the control group). What the primary endpoint will be is decided before the study begins. (NCI)
Prospective
In medicine, a study or clinical trial in which participants are identified and then followed forward in time. (NCI)
Prospective cohort study
A research study that follows over time groups of individuals who are alike in many ways but differ by a certain characteristic (for example, female nurses who smoke and those who do not smoke) and compares them for a particular outcome. (NCI)
Clinical trial protocol
A study plan on which all clinical trials are based. The plan is carefully designed to safeguard the health of the participants as well as answer specific research questions. A protocol describes what types of people may participate in the trial; the schedule of tests, procedures, medications, and dosages; and the length of the study. While in a clinical trial, participants following a protocol are seen regularly by the research staff to monitor their health and to determine the safety and effectiveness of their treatment (NLM)
An action plan for a clinical trial. The plan states what the study will do, how, and why. It explains how many people will be in it, who is eligible to participate, what study agents or other interventions they will be given, what tests they will receive and how often, and what information will be gathered. (NCI)
A document that describes the objective(s), design, methodology, statistical considerations, and organization of a trial. The protocol usually also gives the background and rationale for the trial, but these could be provided in other protocol referenced documents. Throughout the ICH GCP Guidance, the term protocol refers to protocol and protocol amendments. (ICH E6)
Protocol Amendment
A written description of a change(s) to or formal clarification of a protocol. (ICH E6)
Q
Quality Assurance
All those planned and systematic actions that are established to ensure that the trial is performed and the data are generated, documented (recorded), and reported in compliance with GCP and the applicable regulatory requirement(s). (ICH E6)
Quality Control
The operational techniques and activities undertaken within the quality assurance system to verify that the requirements for quality of the trial related activities have been fulfilled. (ICH E6)
Quality of life trials (or supportive care trials)
Refers to trials that explore ways to improve comfort and quality of life for individuals with a chronic illness. (NLM)
R
Randomization
A method based on chance by which study participants are assigned to a treatment group. Randomization minimizes the differences among groups by equally distributing people with particular characteristics among all the trial arms. The researchers do not know which treatment is better. From what is known at the time, any one of the treatments chosen could be of benefit to the participant (NLM)
When referring to an experiment or clinical trial, the process by which animal or human subjects are assigned by chance to separate groups that compare different treatments or other interventions. Randomization gives each participant an equal chance of being assigned to any of the groups. (NCI)
The process of assigning trial subjects to treatment or control groups using an element of chance to determine the assignments in order to reduce bias. (ICH E6)
Randomized clinical trial
A study in which the participants are assigned by chance to separate groups that compare different treatments; neither the researchers nor the participants can choose which group. Using chance to assign people to groups means that the groups will be similar and that the treatments they receive can be compared objectively. At the time of the trial, it is not known which treatment is best. It is the patient's choice to be in a randomized trial. (NCI)
A study in which participants are randomly (i.e., by chance) assigned to one of two or more treatment arms of a clinical trial. Occasionally placebos are utilized. (NLM)
Recruiting
The period during which a trial is attempting to identify and enroll participants. Recruitment activities can include advertising and other ways of soliciting interest from possible participants (NLM)
Recruitment status
Indicates the current stage of a trial, whether it is planned, ongoing, or completed. (NLM)
Regimen
A treatment plan that specifies the dosage, the schedule, and the duration of treatment. (NCI)
Regulatory Authorities
Bodies having the power to regulate. In the ICH GCP guidance, the expression "Regulatory Authorities" includes the authorities that review submitted clinical data and those that conduct inspections. These bodies are sometimes referred to as competent authorities. (ICH E6)
Retrospective
Looking back at events that have already taken place. (NCI)
Retrospective cohort study
A research study in which the medical records of groups of individuals who are alike in many ways but differ by a certain characteristic (for example, female nurses who smoke and those who do not smoke) are compared for a particular outcome. Also called a historic cohort study. (NCI)
Retrospective study
A study that compares two groups of people: those with the disease or condition under study (cases) and a very similar group of people who do not have the disease or condition (controls). Researchers study the medical and lifestyle histories of the people in each group to learn what factors may be associated with the disease or condition. For example, one group may have been exposed to a particular substance that the other was not. Also called a case-control study. (NCI)
Risk-benefit ratio
The risk to individual participants versus the potential benefits. The risk/benefit ratio may differ depending on the condition being treated. (NLM)
S
Safety & tolerability
The safety of a medical product concerns the medical risk to the subject, usually assessed in a clinical trial by laboratory tests (including clinical chemistry and haematology), vital signs, clinical adverse events (diseases, signs and symptoms), and other special safety tests (e.g. ECGs, ophthalmology). The tolerability of the medical product represents the degree to which overt adverse effects can be tolerated by the subject. (ICH E9)
Screening trials
Refers to trials which test the best way to detect certain diseases or health conditions. (NLM)
Selection bias
An error in choosing the individuals or groups to take part in a study. Ideally, the subjects in a study should be very similar to one another and to the larger population from which they are drawn (for example, all individuals with the same disease or condition). If there are important differences, the results of the study may not be valid. (NCI)
Serious Adverse Event
Any untoward medical occurrence that at any dose: results in death, is life-threatening, requires inpatient hospitalization or prolongation of existing hospitalization, results in persistent or significant disability/incapacity, or is a congenital anomaly/birth defect. (ICH E6)
Sham therapy
An inactive treatment or procedure that is intended to mimic as closely as possible a therapy in a clinical trial. Also called placebo therapy. (NCI)
Side effect
A problem that occurs when treatment affects healthy tissues or organs. (NCI)
Any undesired actions or effects of a drug or treatment. Negative or adverse effects may include headache, nausea, hair loss, skin irritation, or other physical problems. Experimental drugs must be evaluated for both immediate and long-term side effects (NLM)
Significant
In statistics, describes a mathematical measure of difference between groups. The difference is said to be significant if it is greater than what might be expected to happen by chance alone. Also called statistically significant. (NCI)
Single blind study
A type of clinical trial in which only the doctor knows whether a patient is taking the standard treatment or the new treatment being tested. This helps prevent bias in treatment studies. (NCI)
A study in which one party, either the investigator or participant, is unaware of what medication the participant is taking; also called single-masked study. (NLM)
Source Data
All information in original records and certified copies of original records of clinical findings, observations, or other activities in a clinical trial necessary for the reconstruction and evaluation of the trial. Source data are contained in source documents (original records or certified copies). (ICH E6)
Source Documents
Original documents, data, and records (e.g., hospital records, clinical and office charts, laboratory notes, memoranda, subjects' diaries or evaluation checklists, pharmacy dispensing records, recorded data from automated instruments, copies or transcriptions certified after verification as being accurate and complete, microfiches, photographic negatives, microfilm or magnetic media, x-rays, subject files, and records kept at the pharmacy, at the laboratories, and at medico-technical departments involved in the clinical trial). (ICH E6)
Sponsor
An individual, company, institution, or organization that takes responsibility for the initiation, management, and/or financing of a clinical trial. (ICH E6)
A person who initiates a clinical investigation, but who does not actually conduct the investigation, i.e., the test article is administered or dispensed to or used involving, a subject under the immediate direction of another individual. A person other than an individual (e.g., corporation or agency) that uses one or more of its own employees to conduct a clinical investigation it has initiated is considered to be a sponsor (not a sponsor-investigator), and the employees are considered to be investigators. (21CFR50.3)
Sponsor-Investigator
An individual who both initiates and conducts, alone or with others, a clinical trial, and under whose immediate direction the investigational product is administered to, dispensed to, or used by a subject. The term does not include any person other than an individual (e.g., it does not include a corporation or an agency). The obligations of a sponsor-investigator include both those of a sponsor and those of an investigator. (ICH E6)
An individual who both initiates and actually conducts, alone or with others, a clinical investigation, i.e., under whose immediate direction the test article is administered or dispensed to, or used involving, a subject. The term does not include any person other than an individual, e.g., corporation or agency. (21CFR50.3)
Standard treatment
A treatment currently in wide use and approved by the FDA, considered to be effective in the treatment of a specific disease or condition. (NLM)
Standards of care
Treatment regimen or medical management based on state of the art participant care. (NLM)
Standard Operating Procedures
Detailed, written instructions to achieve uniformity of the performance of a specific function. (ICH E6)
Statistical analysis plan
A statistical analysis plan is a document that contains a more technical and detailed elaboration of the principal features of the analysis described in the protocol, and includes detailed procedures for executing the statistical analysis of the primary and secondary variables and other data. (ICH E9)
Statistical significance
The probability that an event or difference occurred by chance alone. In clinical trials, the level of statistical significance depends on the number of participants studied and the observations made, as well as the magnitude of differences observed. (NLM)
Study endpoint
A primary or secondary outcome used to judge the effectiveness of a treatment. (NLM)
Study type
The primary investigative techniques used in an observational protocol; types are Purpose, Duration, Selection, and Timing. (NLM)
Subinvestigator
Any individual member of the clinical trial team designated and supervised by the investigator at a trial site to perform critical trial-related procedures and/or to make important trial-related decisions (e.g., associates, residents, research fellows). (ICH E6)
Subject Identification Code
A unique identifier assigned by the investigator to each trial subject to protect the subject's identity and used in lieu of the subject's name when the investigator reports adverse events and/or other trial-related data. (ICH E6)
Subject/Trial Subject
An individual who participates in a clinical trial, either as a recipient of the investigational product(s) or as a control. (ICH E6)
Superiority trial
A trial with the primary objective of showing that the response to the investigational product is superior to a comparative agent (active or placebo control). (ICH E9)
Surrogate variable
A variable that provides an indirect measurement of effect in situations where direct measurement of clinical effect is not feasible or practical. (ICH E9)
T
Test article
Any drug (including a biological product for human use), medical device for human use, human food additive, color additive, electronic product, or any other article subject to regulation under the FD&C Act (21CFR50.3)
Toxicity
An adverse effect produced by a drug that is detrimental to the participant's health. The level of toxicity associated with a drug will vary depending on the condition which the drug is used to treat. (NLM)
Treatment effect
An effect attributed to a treatment in a clinical trial. In most clinical trials the treatment effect of interest is a comparison (or contrast) of two or more treatments. (ICH E9)
Treatment emergent
An event that emerges during treatment having been absent pre-treatment, or worsens relative to the pre-treatment state. (ICH E9)
Treatment IND
IND stands for Investigational New Drug application, which is part of the process to get approval from the FDA for marketing a new prescription drug in the U.S. It makes promising new drugs available to desperately ill participants as early in the drug development process as possible. Treatment INDs are made available to participants before general marketing begins, typically during Phase III studies. To be considered for a treatment IND a participant cannot be eligible to be in the definitive clinical trial. (NLM)
Treatment trials
Refers to trials which test new treatments, new combinations of drugs, or new approaches to surgery or radiation therapy. (NLM)
Trial Site
The location(s) where trial-related activities are actually conducted. (ICH E6)
Trial statistician
A statistician who has a combination of education/training and experience sufficient to implement the principles in this guidance and who is responsible for the statistical aspects of the trial. (ICH E9)
t-test
A statistical test that is used to find out if there is a real difference between the means (averages) of two different groups. It is sometimes used to see if there is a significant difference in response to treatment between groups in a clinical trial. (NCI)
U
Uncontrolled study-A clinical study that lacks a comparison (i.e., a control) group. (NCI)
Unexpected Adverse Drug Reaction-An adverse reaction, the nature or severity of which is not consistent with the applicable product information (e.g., Investigator's Brochure for an unapproved investigational product or package insert/summary of product characteristics for an approved product). (ICH E6)
V
Vulnerable Subjects- Individuals whose willingness to volunteer in a clinical trial may be unduly influenced by the expectation, whether justified or not, of benefits associated with participation, or of a retaliatory response from senior members of a hierarchy in case of refusal to participate. Examples are members of a group with a hierarchical structure, such as medical, pharmacy, dental, and nursing students, subordinate hospital and laboratory personnel, employees of the pharmaceutical industry, members of the armed forces, and persons kept in detention. Other vulnerable subjects include patients with incurable diseases, persons in nursing homes, unemployed or impoverished persons, patients in emergency situations, ethnic minority groups, homeless persons, nomads, refugees, minors, and those incapable of giving consent. (ICH E6)
W
Well-being of the trial subjects- The physical and mental integrity of the subjects participating in a clinical trial. (ICH E6)
A
abstract data type (ADT)
A mathematical model for data types in which a data type is defined by its behavior (semantics) from the point of view of a user of the data, specifically in terms of possible values, possible operations on data of this type, and the behavior of these operations. This contrasts with data structures, which are concrete representations of data from the point of view of an implementer rather than a user.
abstract method
One with only a signature and no implementation body. It is often used to specify that a subclass must provide an implementation of the method. Abstract methods are used to specify interfaces in some computer languages.[1]
abstraction
1. In software engineering and computer science, the process of removing physical, spatial, or temporal details[2] or attributes in the study of objects or systems in order to more closely attend to other details of interest;[3] it is also very similar in nature to the process of generalization.
2. The result of this process: an abstract concept-object created by keeping common features or attributes to various concrete objects or systems of study.[3]
agent architecture
A blueprint for software agents and intelligent control systems depicting the arrangement of components. The architectures implemented by intelligent agents are referred to as cognitive architectures.[4]
agent-based model (ABM)
A class of computational models for simulating the actions and interactions of autonomous agents (both individual or collective entities such as organizations or groups) with a view to assessing their effects on the system as a whole. It combines elements of game theory, complex systems, emergence, computational sociology, multi-agent systems, and evolutionary programming. Monte Carlo methods are used to introduce randomness.
aggregate function
In database management, a function in which the values of multiple rows are grouped together to form a single value of more significant meaning or measurement, such as a set, a bag, or a list.
agile software development
An approach to software development under which requirements and solutions evolve through the collaborative effort of self-organizing and cross-functional teams and their customer(s)/end user(s).[5] It advocates adaptive planning, evolutionary development, early delivery, and continual improvement, and it encourages rapid and flexible response to change.[6]
algorithm
An unambiguous specification of how to solve a class of problems. Algorithms can perform calculation, data processing, and automated reasoning tasks. They are ubiquitous in computing technologies.
algorithm design
A method or mathematical process for problem-solving and for engineering algorithms. The design of algorithms is part of many solution theories of operation research, such as dynamic programming and divide-and-conquer. Techniques for designing and implementing algorithm designs are also called algorithm design patterns,[7] such as the template method pattern and decorator pattern.
algorithmic efficiency
A property of an algorithm which relates to the number of computational resources used by the algorithm. An algorithm must be analyzed to determine its resource usage, and the efficiency of an algorithm can be measured based on usage of different resources. Algorithmic efficiency can be thought of as analogous to engineering productivity for a repeating or continuous process.
American Standard Code for Information Interchange (ASCII)
A character encoding standard for electronic communications. ASCII codes represent text in computers, telecommunications equipment, and other devices. Most modern character-encoding schemes are based on ASCII, although they support many additional characters.
application programming interface (API)
A set of subroutine definitions, communication protocols, and tools for building software. In general terms, it is a set of clearly defined methods of communication among various components. A good API makes it easier to develop a computer program by providing all the building blocks, which are then put together by the programmer.
application software
Also simply application or app.
Computer software designed to perform a group of coordinated functions, tasks, or activities for the benefit of the user. Common examples of applications include word processors, spreadsheets, accounting applications, web browsers, media players, aeronautical flight simulators, console games, and photo editors. This contrasts with system software, which is mainly involved with managing the computer's most basic running operations, often without direct input from the user. The collective noun application software refers to all applications collectively.[8]
array data structure
Also simply array.
A data structure consisting of a collection of elements (values or variables), each identified by at least one array index or key. An array is stored such that the position of each element can be computed from its index tuple by a mathematical formula.[9][10][11] The simplest type of data structure is a linear array, also called a one-dimensional array.
artifact
One of many kinds of tangible by-products produced during the development of software. Some artifacts (e.g. use cases, class diagrams, and other Unified Modeling Language (UML) models, requirements, and design documents) help describe the function, architecture, and design of software. Other artifacts are concerned with the process of development itself—such as project plans, business cases, and risk assessments.
artificial intelligence (AI)
Also machine intelligence.
Intelligence demonstrated by machines, in contrast to the natural intelligence displayed by humans and other animals. In computer science, AI research is defined as the study of "intelligent agents": devices capable of perceiving their environment and taking actions that maximize the chance of successfully achieving their goals.[12] Colloquially, the term "artificial intelligence" is applied when a machine mimics "cognitive" functions that humans associate with other human minds, such as "learning" and "problem solving".[13]
ASCII
See American Standard Code for Information Interchange.
assertion
In computer programming, a statement that a predicate (Boolean-valued function, i.e. a true–false expression) is always true at that point in code execution. It can help a programmer read the code, help a compiler compile it, or help the program detect its own defects. For the latter, some programs check assertions by actually evaluating the predicate as they run and if it is not in fact true – an assertion failure – the program considers itself to be broken and typically deliberately crashes or throws an assertion failure exception.
associative array
An associative array, map, symbol table, or dictionary is an abstract data type composed of a collection of (key, value) pairs, such that each possible key appears at most once in the collection. Operations associated with this data type allow:[14][15]
the addition of a pair to the collection
the removal of a pair from the collection
the modification of an existing pair
the lookup of a value associated with a particular key
automata theory
The study of abstract machines and automata, as well as the computational problems that can be solved using them. It is a theory in theoretical computer science and discrete mathematics (a subject of study in both mathematics and computer science).
automated reasoning
An area of computer science and mathematical logic dedicated to understanding different aspects of reasoning. The study of automated reasoning helps produce computer programs that allow computers to reason completely, or nearly completely, automatically. Although automated reasoning is considered a sub-field of artificial intelligence, it also has connections with theoretical computer science, and even philosophy.
B
bandwidth
The maximum rate of data transfer across a given path. Bandwidth may be characterized as network bandwidth,[16] data bandwidth,[17] or digital bandwidth.[18][19]
Bayesian programming
A formalism and a methodology for having a technique to specify probabilistic models and solve problems when less than the necessary information is available.
benchmark
The act of running a computer program, a set of programs, or other operations, in order to assess the relative performance of an object, normally by running a number of standard tests and trials against it.[20] The term benchmark is also commonly utilized for the purposes of elaborately designed benchmarking programs themselves.
best, worst and average case
Expressions of what the resource usage is at least, at most, and on average, respectively, for a given algorithm. Usually the resource being considered is running time, i.e. time complexity, but it could also be memory or some other resource. Best case is the function which performs the minimum number of steps on input data of n elements; worst case is the function which performs the maximum number of steps on input data of size n; average case is the function which performs an average number of steps on input data of n elements.
big data
A term used to refer to data sets that are too large or complex for traditional data-processing application software to adequately deal with. Data with many cases (rows) offer greater statistical power, while data with higher complexity (more attributes or columns) may lead to a higher false discovery rate.[21]
big O notation
A mathematical notation that describes the limiting behavior of a function when the argument tends towards a particular value or infinity. It is a member of a family of notations invented by Paul Bachmann,[22] Edmund Landau,[23] and others, collectively called Bachmann–Landau notation or asymptotic notation.
binary number
In mathematics and digital electronics, a number expressed in the base-2 numeral system or binary numeral system, which uses only two symbols: typically 0 (zero) and 1 (one).
binary search algorithm
Also simply binary search, half-interval search,[24] logarithmic search,[25] or binary chop.[26]
A search algorithm that finds the position of a target value within a sorted array.[27][28]
binary tree
A tree data structure in which each node has at most two children, which are referred to as the left child and the right child. A recursive definition using just set theory notions is that a (non-empty) binary tree is a tuple (L, S, R), where L and R are binary trees or the empty set and S is a singleton set.[29] Some authors allow the binary tree to be the empty set as well.[30]
bioinformatics
An interdisciplinary field that combines biology, computer science, information engineering, mathematics, and statistics to develop methods and software tools for analyzing and interpreting biological data. Bioinformatics is widely used for in silico analyses of biological queries using mathematical and statistical techniques.
bit
A basic unit of information used in computing and digital communications; a portmanteau of binary digit. A binary digit can have one of two possible values, and may be physically represented with a two-state device. These state values are most commonly represented as either a 0or1.[31]
bit rate (R)
Also bitrate.
In telecommunications and computing, the number of bits that are conveyed or processed per unit of time.[32]
blacklist
Also block list.
In computing, a basic access control mechanism that allows through all elements (email addresses, users, passwords, URLs, IP addresses, domain names, file hashes, etc.), except those explicitly mentioned in a list of prohibited elements. Those items on the list are denied access. The opposite is a whitelist, which means only items on the list are allowed through whatever gate is being used while all other elements are blocked. A greylist contains items that are temporarily blocked (or temporarily allowed) until an additional step is performed.
BMP file format
Also bitmap image file, device independent bitmap (DIB) file format, or simply bitmap.
A raster graphics image file format used to store bitmap digital images independently of the display device (such as a graphics adapter), used especially on Microsoft Windows[33] and OS/2[34] operating systems.
Boolean data type
A data type that has one of two possible values (usually denoted true and false), intended to represent the two truth values of logic and Boolean algebra. It is named after George Boole, who first defined an algebraic system of logic in the mid-19th century. The Boolean data type is primarily associated with conditional statements, which allow different actions by changing control flow depending on whether a programmer-specified Boolean condition evaluates to true or false. It is a special case of a more general logical data type (see probabilistic logic)—i.e. logic need not always be Boolean.
Boolean expression
An expression used in a programming language that returns a Boolean value when evaluated, that is one of true or false. A Boolean expression may be composed of a combination of the Boolean constants true or false, Boolean-typed variables, Boolean-valued operators, and Boolean-valued functions.[35]
Boolean algebra
In mathematics and mathematical logic, the branch of algebra in which the values of the variables are the truth values true and false, usually denoted 1 and 0, respectively. Contrary to elementary algebra, where the values of the variables are numbers and the prime operations are addition and multiplication, the main operations of Boolean algebra are the conjunction and (denoted as ∧), the disjunction or (denoted as ∨), and the negation not (denoted as ¬). It is thus a formalism for describing logical relations in the same way that elementary algebra describes numeric relations.
byte
A unit of digital information that most commonly consists of eight bits, representing a binary number. Historically, the byte was the number of bits used to encode a single character of text in a computer[36][37] and for this reason it is the smallest addressable unit of memory in many computer architectures.
booting
The procedures implemented in starting up a computer or computer appliance until it can be used. It can be initiated by hardware such as a button press or by a software command. After the power is switched on, the computer is relatively dumb and can read only part of its storage called read-only memory. There, a small program is stored called firmware. It does power-on self-tests and, most importantly, allows access to other types of memory like a hard disk and main memory. The firmware loads bigger programs into the computer's main memory and runs it.
C
callback
Also a call-after function.[38]
Any executable code that is passed as an argument to other code that is expected to "call back" (execute) the argument at a given time. This execution may be immediate, as in a synchronous callback, or it might happen at a later time, as in an asynchronous callback.
central processing unit (CPU)
The electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logic, controlling, and input/output (I/O) operations specified by the instructions. The computer industry has used the term "central processing unit" at least since the early 1960s.[39] Traditionally, the term "CPU" refers to a processor, more specifically to its processing unit and control unit (CU), distinguishing these core elements of a computer from external components such as main memory and I/O circuitry.[40]
character
A unit of information that roughly corresponds to a grapheme, grapheme-like unit, or symbol, such as in an alphabet or syllabary in the written form of a natural language.[41]
cipher
Also cypher.
In cryptography, an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure.
class
In object-oriented programming, an extensible program-code-template for creating objects, providing initial values for state (member variables) and implementations of behavior (member functions or methods).[42][43] In many languages, the class name is used as the name for the class (the template itself), the name for the default constructor of the class (a subroutine that creates objects), and as the type of objects generated by instantiating the class; these distinct concepts are easily conflated.[43]
class-based programming
Also class-orientation.
A style of object-oriented programming (OOP) in which inheritance occurs via defining "classes" of objects, instead of via the objects alone. Compare prototype-based programming.
class-orientation
A style of Object-oriented programming (OOP) in which inheritance occurs via defining classes of objects, instead of inheritance occurring via the objects alone (compare prototype-based programming).
client
A piece of computer hardware or software that accesses a service made available by a server. The server is often (but not always) on another computer system, in which case the client accesses the service by way of a network.[44] The term applies to the role that programs or devices play in the client–server model.
cleanroom software engineering
A software development process intended to produce software with a certifiable level of reliability. The cleanroom process was originally developed by Harlan Mills and several of his colleagues including Alan Hevner at IBM.[45] The focus of the cleanroom process is on defect prevention, rather than defect removal.
closure
Also lexical closure or function closure.
A technique for implementing lexically scoped name binding in a language with first-class functions. Operationally, a closure is a record storing a function[a] together with an environment.[46]
cloud computing
Shared pools of configurable computer system resources and higher-level services that can be rapidly provisioned with minimal management effort, often over the Internet. Cloud computing relies on sharing of resources to achieve coherence and economies of scale, similar to a public utility.
code library
A collection of non-volatile resources used by computer programs, often for software development. These may include configuration data, documentation, help data, message templates, pre-written code and subroutines, classes, values or type specifications. In IBM's OS/360 and its successors they are referred to as partitioned data sets.
coding
Computer programming is the process of designing and building an executable computer program for accomplishing a specific computing task. Programming involves tasks such as analysis, generating algorithms, profiling algorithms' accuracy and resource consumption, and the implementation of algorithms in a chosen programming language (commonly referred to as coding[47][48]). The source code of a program is written in one or more programming languages. The purpose of programming is to find a sequence of instructions that will automate the performance of a task for solving a given problem. The process of programming thus often requires expertise in several different subjects, including knowledge of the application domain, specialized algorithms, and formal logic.
coding theory
The study of the properties of codes and their respective fitness for specific applications. Codes are used for data compression, cryptography, error detection and correction, data transmission and data storage. Codes are studied by various scientific disciplines—such as information theory, electrical engineering, mathematics, linguistics, and computer science—for the purpose of designing efficient and reliable data transmission methods. This typically involves the removal of redundancy and the correction or detection of errors in the transmitted data.
cognitive science
The interdisciplinary, scientific study of the mind and its processes.[49] It examines the nature, the tasks, and the functions of cognition (in a broad sense). Cognitive scientists study intelligence and behavior, with a focus on how nervous systems represent, process, and transform information. Mental faculties of concern to cognitive scientists include language, perception, memory, attention, reasoning, and emotion; to understand these faculties, cognitive scientists borrow from fields such as linguistics, psychology, artificial intelligence, philosophy, neuroscience, and anthropology.[50]
collection
A collection or container is a grouping of some variable number of data items (possibly zero) that have some shared significance to the problem being solved and need to be operated upon together in some controlled fashion. Generally, the data items will be of the same type or, in languages supporting inheritance, derived from some common ancestor type. A collection is a concept applicable to abstract data types, and does not prescribe a specific implementation as a concrete data structure, though often there is a conventional choice (see Container for type theory discussion).
comma-separated values (CSV)
A delimited text file that uses a comma to separate values. A CSV file stores tabular data (numbers and text) in plain text. Each line of the file is a data record. Each record consists of one or more fields, separated by commas. The use of the comma as a field separator is the source of the name for this file format.
compiler
A computer program that transforms computer code written in one programming language (the source language) into another programming language (the target language). Compilers are a type of translator that support digital devices, primarily computers. The name compiler is primarily used for programs that translate source code from a high-level programming language to a lower-level language (e.g. assembly language, object code, or machine code) to create an executable program.[51]
computability theory
also known as recursion theory, is a branch of mathematical logic, of computer science, and of the theory of computation that originated in the 1930s with the study of computable functions and Turing degrees. The field has since expanded to include the study of generalized computability and definability. In these areas, recursion theory overlaps with proof theory and effective descriptive set theory.
computation
Any type of calculation[52][53] that includes both arithmetical and non-arithmetical steps and follows a well-defined model, e.g. an algorithm. The study of computation is paramount to the discipline of computer science.
computational biology
Involves the development and application of data-analytical and theoretical methods, mathematical modelling and computational simulation techniques to the study of biological, ecological, behavioural, and social systems.[54] The field is broadly defined and includes foundations in biology, applied mathematics, statistics, biochemistry, chemistry, biophysics, molecular biology, genetics, genomics, computer science, and evolution.[55] Computational biology is different from biological computing, which is a subfield of computer science and computer engineering using bioengineering and biology to build computers.
computational chemistry
A branch of chemistry that uses computer simulation to assist in solving chemical problems. It uses methods of theoretical chemistry, incorporated into efficient computer programs, to calculate the structures and properties of molecules and solids.
computational complexity theory
A subfield of computational science which focuses on classifying computational problems according to their inherent difficulty, and relating these classes to each other. A computational problem is a task solved by a computer. A computation problem is solvable by mechanical application of mathematical steps, such as an algorithm.
computational model
A mathematical model in computational science that requires extensive computational resources to study the behavior of a complex system by computer simulation.[56]
computational neuroscience
Also theoretical neuroscience or mathematical neuroscience.
A branch of neuroscience which employs mathematical models, theoretical analysis, and abstractions of the brain to understand the principles that govern the development, structure, physiology, and cognitive abilities of the nervous system.[57][58][59][60]
computational physics
Is the study and implementation of numerical analysis to solve problems in physics for which a quantitative theory already exists.[61] Historically, computational physics was the first application of modern computers in science, and is now a subset of computational science.
computational science
Also scientific computing and scientific computation (SC).
An interdisciplinary field that uses advanced computing capabilities to understand and solve complex problems. It is an area of science which spans many disciplines, but at its core it involves the development of computer models and simulations to understand complex natural systems.
computational steering
Is the practice of manually intervening with an otherwise autonomous computational process, to change its outcome.
computer
A device that can be instructed to carry out sequences of arithmetic or logical operations automatically via computer programming. Modern computers have the ability to follow generalized sets of operations, called programs. These programs enable computers to perform an extremely wide range of tasks.
computer architecture
A set of rules and methods that describe the functionality, organization, and implementation of computer systems. Some definitions of architecture define it as describing the capabilities and programming model of a computer but not a particular implementation.[62] In other definitions computer architecture involves instruction set architecture design, microarchitecture design, logic design, and implementation.[63]
computer data storage
Also simply storage or memory.
A technology consisting of computer components and recording media that are used to retain digital data. Data storage is a core function and fundamental component of all modern computer systems.[64]:15–16
computer ethics
A part of practical philosophy concerned with how computing professionals should make decisions regarding professional and social conduct.[65]
computer graphics
Pictures and films created using computers. Usually, the term refers to computer-generated image data created with the help of specialized graphical hardware and software. It is a vast and recently developed area of computer science.
computer network
Also data network.
A digital telecommunications network which allows nodes to share resources. In computer networks, computing devices exchange data with each other using connections (data links) between nodes. These data links are established over cable media such as wires or optic cables, or wireless media such as Wi-Fi.
computer program
Is a collection of instructions[66] that can be executed by a computer to perform a specific task.
computer programming
The process of designing and building an executable computer program for accomplishing a specific computing task. Programming involves tasks such as analysis, generating algorithms, profiling algorithms' accuracy and resource consumption, and the implementation of algorithms in a chosen programming language (commonly referred to as coding[47][48]). The source code of a program is written in one or more programming languages. The purpose of programming is to find a sequence of instructions that will automate the performance of a task for solving a given problem. The process of programming thus often requires expertise in several different subjects, including knowledge of the application domain, specialized algorithms, and formal logic.
computer science
The theory, experimentation, and engineering that form the basis for the design and use of computers. It involves the study of algorithms that process, store, and communicate digital information. A computer scientist specializes in the theory of computation and the design of computational systems.[67]
computer scientist
A person who has acquired the knowledge of computer science, the study of the theoretical foundations of information and computation and their application.[68]
computer security
Also cybersecurity[69] or information technology security (IT security).
The protection of computer systems from theft or damage to their hardware, software, or electronic data, as well as from disruption or misdirection of the services they provide.
computer vision
An interdisciplinary scientific field that deals with how computers can be made to gain high-level understanding from digital images or videos. From the perspective of engineering, it seeks to automate tasks that the human visual system can do.[70][71][72]
computing
Is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes study of algorithmic processes and development of both hardware and software. It has scientific, engineering, mathematical, technological and social aspects. Major computing fields include computer engineering, computer science, cybersecurity, data science, information systems, information technology and software engineering.[73]
concatenation
In formal language theory and computer programming, string concatenation is the operation of joining character strings end-to-end. For example, the concatenation of "snow" and "ball" is "snowball". In certain formalisations of concatenation theory, also called string theory, string concatenation is a primitive notion.
Concurrency
The ability of different parts or units of a program, algorithm, or problem to be executed out-of-order or in partial order, without affecting the final outcome. This allows for parallel execution of the concurrent units, which can significantly improve overall speed of the execution in multi-processor and multi-core systems. In more technical terms, concurrency refers to the decomposability property of a program, algorithm, or problem into order-independent or partially-ordered components or units.[74]
conditional
Also conditional statement, conditional expression, and conditional construct.
A feature of a programming language which performs different computations or actions depending on whether a programmer-specified Boolean condition evaluates to true or false. Apart from the case of branch predication, this is always achieved by selectively altering the control flow based on some condition.
container
Is a class, a data structure,[75][76] or an abstract data type (ADT) whose instances are collections of other objects. In other words, they store objects in an organized way that follows specific access rules. The size of the container depends on the number of objects (elements) it contains. Underlying (inherited) implementations of various container types may vary in size and complexity, and provide flexibility in choosing the right implementation for any given scenario.
continuation-passing style (CPS)
A style of functional programming in which control is passed explicitly in the form of a continuation. This is contrasted with direct style, which is the usual style of programming. Gerald Jay Sussman and Guy L. Steele, Jr. coined the phrase in AI Memo 349 (1975), which sets out the first version of the Scheme programming language.[77][78]
control flow
Also flow of control.
The order in which individual statements, instructions or function calls of an imperative program are executed or evaluated. The emphasis on explicit control flow distinguishes an imperative programming language from a declarative programming language.
Creative Commons (CC)
An American non-profit organization devoted to expanding the range of creative works available for others to build upon legally and to share.[79] The organization has released several copyright-licenses, known as Creative Commons licenses, free of charge to the public.
cryptography
Or cryptology, is the practice and study of techniques for secure communication in the presence of third parties called adversaries.[80] More generally, cryptography is about constructing and analyzing protocols that prevent third parties or the public from reading private messages;[81] various aspects in information security such as data confidentiality, data integrity, authentication, and non-repudiation[82] are central to modern cryptography. Modern cryptography exists at the intersection of the disciplines of mathematics, computer science, electrical engineering, communication science, and physics. Applications of cryptography include electronic commerce, chip-based payment cards, digital currencies, computer passwords, and military communications.
CSV
See comma-separated values.
cyberbullying
Also cyberharassment or online bullying.
A form of bullying or harassment using electronic means.
cyberspace
Widespread, interconnected digital technology.
D
daemon
In multitasking computer operating systems, a daemon (/ˈdiːmən/ or /ˈdeɪmən/)[83] is a computer program that runs as a background process, rather than being under the direct control of an interactive user. Traditionally, the process names of a daemon end with the letter d, for clarification that the process is in fact a daemon, and for differentiation between a daemon and a normal computer program. For example, syslogd is a daemon that implements system logging facility, and sshd is a daemon that serves incoming SSH connections.
data center
Also data centre.
A dedicated space used to house computer systems and associated components, such as telecommunications and data storage systems. It generally includes redundant or backup components and infrastructure for power supply, data communications connections, environmental controls (e.g. air conditioning and fire suppression) and various security devices.[84][85]
database
An organized collection of data, generally stored and accessed electronically from a computer system. Where databases are more complex, they are often developed using formal design and modeling techniques.
data mining
Is a process of discovering patterns in large data sets involving methods at the intersection of machine learning, statistics, and database systems.[86] Data mining is an interdisciplinary subfield of computer science and statistics with an overall goal to extract information (with intelligent methods) from a data set and transform the information into a comprehensible structure for further use.[86][87][88][89] Data mining is the analysis step of the "knowledge discovery in databases" process, or KDD.[90] Aside from the raw analysis step, it also involves database and data management aspects, data pre-processing, model and inference considerations, interestingness metrics, complexity considerations, post-processing of discovered structures, visualization, and online updating.[86]
data science
An interdisciplinary field that uses scientific methods, processes, algorithms, and systems to extract knowledge and insights from data in various forms, both structured and unstructured,[91][92] similar to data mining. Data science is a "concept to unify statistics, data analysis, machine learning and their related methods" in order to "understand and analyze actual phenomena" with data.[93] It employs techniques and theories drawn from many fields within the context of mathematics, statistics, information science, and computer science.
data structure
A data organization, management, and storage format that enables efficient access and modification.[94][95][96] More precisely, a data structure is a collection of data values, the relationships among them, and the functions or operations that can be applied to the data.[97]
data type
Also simply type.
An attribute of data which tells the compiler or interpreter how the programmer intends to use the data. Most programming languages support common data types of real, integer, and Boolean. A data type constrains the values that an expression, such as a variable or a function, might take. This data type defines the operations that can be done on the data, the meaning of the data, and the way values of that type can be stored. A type of value from which an expression may take its value.[98][99]
debugging
The process of finding and resolving defects or problems within a computer program that prevent correct operation of computer software or the system as a whole. Debugging tactics can involve interactive debugging, control flow analysis, unit testing, integration testing, log file analysis, monitoring at the application or system level, memory dumps, and profiling.
declaration
In computer programming, a language construct that specifies properties of an identifier: it declares what a word (identifier) "means".[100] Declarations are most commonly used for functions, variables, constants, and classes, but can also be used for other entities such as enumerations and type definitions.[100] Beyond the name (the identifier itself) and the kind of entity (function, variable, etc.), declarations typically specify the data type (for variables and constants), or the type signature (for functions); types may also include dimensions, such as for arrays. A declaration is used to announce the existence of the entity to the compiler; this is important in those strongly typed languages that require functions, variables, and constants, and their types, to be specified with a declaration before use, and is used in forward declaration.[101] The term "declaration" is frequently contrasted with the term "definition",[100] but meaning and usage varies significantly between languages.
digital data
In information theory and information systems, the discrete, discontinuous representation of information or works. Numbers and letters are commonly used representations.
digital signal processing (DSP)
The use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The signals processed in this manner are a sequence of numbers that represent samples of a continuous variable in a domain such as time, space, or frequency.
discrete event simulation (DES)
A model of the operation of a system as a discrete sequence of events in time. Each event occurs at a particular instant in time and marks a change of state in the system.[102] Between consecutive events, no change in the system is assumed to occur; thus the simulation can directly jump in time from one event to the next.
disk storage
(Also sometimes called drive storage) is a general category of storage mechanisms where data is recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A disk drive is a device implementing such a storage mechanism. Notable types are the hard disk drive (HDD) containing a non-removable disk, the floppy disk drive (FDD) and its removable floppy disk, and various optical disc drives (ODD) and associated optical disc media.
distributed computing
A field of computer science that studies distributed systems. A distributed system is a system whose components are located on different networked computers, which communicate and coordinate their actions by passing messages to one another.[103] The components interact with one another in order to achieve a common goal. Three significant characteristics of distributed systems are: concurrency of components, lack of a global clock, and independent failure of components.[103] Examples of distributed systems vary from SOA-based systems to massively multiplayer online games to peer-to-peer applications.
divide and conquer algorithm
An algorithm design paradigm based on multi-branched recursion. A divide-and-conquer algorithm works by recursively breaking down a problem into two or more sub-problems of the same or related type, until these become simple enough to be solved directly. The solutions to the sub-problems are then combined to give a solution to the original problem.
DNS
See Domain Name System.
documentation
Written text or illustration that accompanies computer software or is embedded in the source code. It either explains how it operates or how to use it, and may mean different things to people in different roles.
domain
Is the targeted subject area of a computer program. It is a term used in software engineering. Formally it represents the target subject of a specific programming project, whether narrowly or broadly defined.[104]
Domain Name System (DNS)
A hierarchical and decentralized naming system for computers, services, or other resources connected to the Internet or to a private network. It associates various information with domain names assigned to each of the participating entities. Most prominently, it translates more readily memorized domain names to the numerical IP addresses needed for locating and identifying computer services and devices with the underlying network protocols. By providing a worldwide, distributed directory service, the Domain Name System has been an essential component of the functionality of the Internet since 1985.
double-precision floating-point format
A computer number format. It represents a wide dynamic range of numerical values by using a floating radix point.
download
In computer networks, to receive data from a remote system, typically a server[105] such as a web server, an FTP server, an email server, or other similar systems. This contrasts with uploading, where data is sent to a remote server. A download is a file offered for downloading or that has been downloaded, or the process of receiving such a file.
E
edge device
A device which provides an entry point into enterprise or service provider core networks. Examples include routers, routing switches, integrated access devices (IADs), multiplexers, and a variety of metropolitan area network (MAN) and wide area network (WAN) access devices. Edge devices also provide connections into carrier and service provider networks. An edge device that connects a local area network to a high speed switch or backbone (such as an ATM switch) may be called an edge concentrator.
encryption
In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decipher a ciphertext back to plaintext and access the original information. Encryption does not itself prevent interference but denies the intelligible content to a would-be interceptor. For technical reasons, an encryption scheme usually uses a pseudo-random encryption key generated by an algorithm. It is possible to decrypt the message without possessing the key, but, for a well-designed encryption scheme, considerable computational resources and skills are required. An authorized recipient can easily decrypt the message with the key provided by the originator to recipients but not to unauthorized users. Historically, various forms of encryption have been used to aid in cryptography. Early encryption techniques were often utilized in military messaging. Since then, new techniques have emerged and become commonplace in all areas of modern computing.[106] Modern encryption schemes utilize the concepts of public-key and symmetric-key.[106] Modern encryption techniques ensure security because modern computers are inefficient at cracking the encryption.
event
An action or occurrence recognized by software, often originating asynchronously from the external environment, that may be handled by the software. Because an event is an entity which encapsulates the action and the contextual variables triggering the action, the acrostic mnemonic "Execution Variable Encapsulating Named Trigger" is often used to clarify the concept.
event-driven programming
A programming paradigm in which the flow of the program is determined by events such as user actions (mouse clicks, key presses), sensor outputs, or messages from other programs or threads. Event-driven programming is the dominant paradigm used in graphical user interfaces and other applications (e.g. JavaScript web applications) that are centered on performing certain actions in response to user input. This is also true of programming for device drivers (e.g. P in USB device driver stacks[107]).
evolutionary computing
A family of algorithms for global optimization inspired by biological evolution, and the subfield of artificial intelligence and soft computing studying these algorithms. In technical terms, they are a family of population-based trial-and-error problem-solvers with a metaheuristic or stochastic optimization character.
executable
Also executable code, executable file, executable program, or simply executable.
Causes a computer "to perform indicated tasks according to encoded instructions,"[108] as opposed to a data file that must be parsed by a program to be meaningful. The exact interpretation depends upon the use - while "instructions" is traditionally taken to mean machine code instructions for a physical CPU, in some contexts a file containing bytecode or scripting language instructions may also be considered executable.
executable module
execution
In computer and software engineering is the process by which a computer or virtual machine executes the instructions of a computer program. Each instruction of a program is a description of a particular action which to be carried out in order for a specific problem to be solved; as instructions of a program and therefore the actions they describe are being carried out by an executing machine, specific effects are produced in accordance to the semantics of the instructions being executed.
exception handling
The process of responding to the occurrence, during computation, of exceptions – anomalous or exceptional conditions requiring special processing – often disrupting the normal flow of program execution. It is provided by specialized programming language constructs, computer hardware mechanisms like interrupts, or operating system IPC facilities like signals.
expression
In a programming language, a combination of one or more constants, variables, operators, and functions that the programming language interprets (according to its particular rules of precedence and of association) and computes to produce ("to return", in a stateful environment) another value. This process, as for mathematical expressions, is called evaluation.
external library
F
fault-tolerant computer system
A system designed around the concept of fault tolerance. In essence, they must be able to continue working to a level of satisfaction in the presence of errors or breakdowns.
feasibility study
An investigation which aims to objectively and rationally uncover the strengths and weaknesses of an existing business or proposed venture, opportunities and threats present in the natural environment, the resources required to carry through, and ultimately the prospects for success.[109][110] In its simplest terms, the two criteria to judge feasibility are cost required and value to be attained.[111]
field
Data that has several parts, known as a record, can be divided into fields. Relational databases arrange data as sets of database records, so called rows. Each record consists of several fields; the fields of all records form the columns. Examples of fields: name, gender, hair colour.
filename extension
An identifier specified as a suffix to the name of a computer file. The extension indicates a characteristic of the file contents or its intended use.
filter (software)
A computer program or subroutine to process a stream, producing another stream. While a single filter can be used individually, they are frequently strung together to form a pipeline.
floating point arithmetic
In computing, floating-point arithmetic (FP) is arithmetic using formulaic representation of real numbers as an approximation to support a trade-off between range and precision. For this reason, floating-point computation is often found in systems which include very small and very large real numbers, which require fast processing times. A number is, in general, represented approximately to a fixed number of significant digits (the significand) and scaled using an exponent in some fixed base; the base for the scaling is normally two, ten, or sixteen. A number that can be represented exactly is of the following form:
significand × base exponent , {\displaystyle {\text{significand}}\times {\text{base}}^{\text{exponent}},} {\text{significand}}\times {\text{base}}^{\text{exponent}},
where significand is an integer, base is an integer greater than or equal to two, and exponent is also an integer. For example:
1.2345 = 12345 ⏟ significand × 10 ⏟ base − 4 ⏞ exponent . {\displaystyle 1.2345=\underbrace {12345} _{\text{significand}}\times \underbrace {10} _{\text{base}}\!\!\!\!\!\!^{\overbrace {-4} ^{\text{exponent}}}.} 1.2345=\underbrace {12345} _{\text{significand}}\times \underbrace {10} _{\text{base}}\!\!\!\!\!\!^{\overbrace {-4} ^{\text{exponent}}}.
for loop
Also for-loop.
A control flow statement for specifying iteration, which allows code to be executed repeatedly. Various keywords are used to specify this statement: descendants of ALGOL use "for", while descendants of Fortran use "do". There are also other possibilities, e.g. COBOL uses "PERFORM VARYING".
formal methods
A set of mathematically based techniques for the specification, development, and verification of software and hardware systems.[112] The use of formal methods for software and hardware design is motivated by the expectation that, as in other engineering disciplines, performing appropriate mathematical analysis can contribute to the reliability and robustness of a design.[113]
formal verification
The act of proving or disproving the correctness of intended algorithms underlying a system with respect to a certain formal specification or property, using formal methods of mathematics.[114]
functional programming
A programming paradigm—a style of building the structure and elements of computer programs–that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data. It is a declarative programming paradigm in that programming is done with expressions or declarations[115] instead of statements.
G
game theory
The study of mathematical models of strategic interaction between rational decision-makers.[116] It has applications in all fields of social science, as well as in logic and computer science. Originally, it addressed zero-sum games, in which each participant's gains or losses are exactly balanced by those of the other participants. Today, game theory applies to a wide range of behavioral relations, and is now an umbrella term for the science of logical decision making in humans, animals, and computers.
garbage in, garbage out (GIGO)
A term used to describe the concept that flawed or nonsense input data produces nonsense output or "garbage".
Graphics Interchange Format
gigabyte
A multiple of the unit byte for digital information. The prefix giga means 109 in the International System of Units (SI). Therefore, one gigabyte is 1000000000bytes. The unit symbol for the gigabyte is GB.
global variable
In computer programming, a variable with global scope, meaning that it is visible (hence accessible) throughout the program, unless shadowed. The set of all global variables is known as the global environment or global state. In compiled languages, global variables are generally static variables, whose extent (lifetime) is the entire runtime of the program, though in interpreted languages (including command-line interpreters), global variables are generally dynamically allocated when declared, since they are not known ahead of time.
graph theory
In mathematics, the study of graphs, which are mathematical structures used to model pairwise relations between objects. A graph in this context is made up of vertices (also called nodes or points) which are connected by edges (also called links or lines). A distinction is made between undirected graphs, where edges link two vertices symmetrically, and directed graphs, where edges link two vertices asymmetrically.
H
handle
In computer programming, a handle is an abstract reference to a resource that is used when application software references blocks of memory or objects that are managed by another system like a database or an operating system.
hard problem
Computational complexity theory focuses on classifying computational problems according to their inherent difficulty, and relating these classes to each other. A computational problem is a task solved by a computer. A computation problem is solvable by mechanical application of mathematical steps, such as an algorithm.
hash function
Any function that can be used to map data of arbitrary size to data of a fixed size. The values returned by a hash function are called hash values, hash codes, digests, or simply hashes. Hash functions are often used in combination with a hash table, a common data structure used in computer software for rapid data lookup. Hash functions accelerate table or database lookup by detecting duplicated records in a large file.
hash table
In computing, a hash table (hash map) is a data structure that implements an associative array abstract data type, a structure that can map keys to values. A hash table uses a hash function to compute an index into an array of buckets or slots, from which the desired value can be found.
heap
A specialized tree-based data structure which is essentially an almost complete[117] tree that satisfies the heap property: if P is a parent node of C, then the key (the value) of P is either greater than or equal to (in a max heap) or less than or equal to (in a min heap) the key of C.[118] The node at the "top" of the heap (with no parents) is called the root node.
heapsort
A comparison-based sorting algorithm. Heapsort can be thought of as an improved selection sort: like that algorithm, it divides its input into a sorted and an unsorted region, and it iteratively shrinks the unsorted region by extracting the largest element and moving that to the sorted region. The improvement consists of the use of a heap data structure rather than a linear-time search to find the maximum.[119]
human-computer interaction (HCI)
Researches the design and use of computer technology, focused on the interfaces between people (users) and computers. Researchers in the field of HCI both observe the ways in which humans interact with computers and design technologies that let humans interact with computers in novel ways. As a field of research, human–computer interaction is situated at the intersection of computer science, behavioral sciences, design, media studies, and several other fields of study.
I
identifier
In computer languages, identifiers are tokens (also called symbols) which name language entities. Some of the kinds of entities an identifier might denote include variables, types, labels, subroutines, and packages.
IDE
Integrated development environment.
image processing
imperative programming
A programming paradigm that uses statements that change a program's state. In much the same way that the imperative mood in natural languages expresses commands, an imperative program consists of commands for the computer to perform. Imperative programming focuses on describing how a program operates.
incremental build model
A method of software development where the product is designed, implemented and tested incrementally (a little more is added each time) until the product is finished. It involves both development and maintenance. The product is defined as finished when it satisfies all of its requirements. This model combines the elements of the waterfall model with the iterative philosophy of prototyping.
information space analysis
A deterministic method, enhanced by machine intelligence, for locating and assessing resources for team-centric efforts.
information visualization
inheritance
In object-oriented programming, the mechanism of basing an object or class upon another object (prototype-based inheritance) or class (class-based inheritance), retaining similar implementation. Also defined as deriving new classes (sub classes) from existing ones (super class or base class) and forming them into a hierarchy of classes.
input/output (I/O)
Also informally io or IO.
The communication between an information processing system, such as a computer, and the outside world, possibly a human or another information processing system. Inputs are the signals or data received by the system and outputs are the signals or data sent from it. The term can also be used as part of an action; to "perform I/O" is to perform an input or output operation.
insertion sort
A simple sorting algorithm that builds the final sorted array (or list) one item at a time.
instruction cycle
Also fetch–decode–execute cycle or simply fetch-execute cycle.
The cycle which the central processing unit (CPU) follows from boot-up until the computer has shut down in order to process instructions. It is composed of three main stages: the fetch stage, the decode stage, and the execute stage.
integer
A datum of integral data type, a data type that represents some range of mathematical integers. Integral data types may be of different sizes and may or may not be allowed to contain negative values. Integers are commonly represented in a computer as a group of binary digits (bits). The size of the grouping varies so the set of integer sizes available varies between different types of computers. Computer hardware, including virtual machines, nearly always provide a way to represent a processor register or memory address as an integer.
integrated development environment (IDE)
A software application that provides comprehensive facilities to computer programmers for software development. An IDE normally consists of at least a source code editor, build automation tools, and a debugger.
integration testing
(sometimes called integration and testing, abbreviated I&T) is the phase in software testing in which individual software modules are combined and tested as a group. Integration testing is conducted to evaluate the compliance of a system or component with specified functional requirements.[120] It occurs after unit testing and before validation testing. Integration testing takes as its input modules that have been unit tested, groups them in larger aggregates, applies tests defined in an integration test plan to those aggregates, and delivers as its output the integrated system ready for system testing.[121]
intellectual property (IP)
A category of legal property that includes intangible creations of the human intellect.[122][123] There are many types of intellectual property, and some countries recognize more than others.[124][125][126][127][128] The most well-known types are copyrights, patents, trademarks, and trade secrets.
intelligent agent
In artificial intelligence, an intelligent agent (IA) refers to an autonomous entity which acts, directing its activity towards achieving goals (i.e. it is an agent), upon an environment using observation through sensors and consequent actuators (i.e. it is intelligent).[129] Intelligent agents may also learn or use knowledge to achieve their goals. They may be very simple or very complex. A reflex machine, such as a thermostat, is considered an example of an intelligent agent.[130]
interface
A shared boundary across which two or more separate components of a computer system exchange information. The exchange can be between software, computer hardware, peripheral devices, humans, and combinations of these.[131] Some computer hardware devices, such as a touchscreen, can both send and receive data through the interface, while others such as a mouse or microphone may only provide an interface to send data to a given system.[132]
internal documentation
Computer software is said to have Internal Documentation if the notes on how and why various parts of code operate is included within the source code as comments. It is often combined with meaningful variable names with the intention of providing potential future programmers a means of understanding the workings of the code. This contrasts with external documentation, where programmers keep their notes and explanations in a separate document.
internet
The global system of interconnected computer networks that use the Internet protocol suite (TCP/IP) to link devices worldwide. It is a network of networks that consists of private, public, academic, business, and government networks of local to global scope, linked by a broad array of electronic, wireless, and optical networking technologies.
internet bot
Also web robot, robot, or simply bot.
A software application that runs automated tasks (scripts) over the Internet.[133] Typically, bots perform tasks that are both simple and structurally repetitive, at a much higher rate than would be possible for a human alone. The largest use of bots is in web spidering (web crawler), in which an automated script fetches, analyzes and files information from web servers at many times the speed of a human.
interpreter
A computer program that directly executes instructions written in a programming or scripting language, without requiring them to have been previously compiled into a machine language program.
invariant
One can encounter invariants that can be relied upon to be true during the execution of a program, or during some portion of it. It is a logical assertion that is always held to be true during a certain phase of execution. For example, a loop invariant is a condition that is true at the beginning and the end of every execution of a loop.
iteration
Is the repetition of a process in order to generate an outcome. The sequence will approach some end point or end value. Each repetition of the process is a single iteration, and the outcome of each iteration is then the starting point of the next iteration. In mathematics and computer science, iteration (along with the related technique of recursion) is a standard element of algorithms.
J
Java
A general-purpose programming language that is class-based, object-oriented[134](although not a pure OO language[135]), and designed to have as few implementation dependencies as possible. It is intended to let application developers "write once, run anywhere" (WORA),[136] meaning that compiled Java code can run on all platforms that support Java without the need for recompilation.[137]
K
kernel
The first section of an operating system to load into memory. As the center of the operating system, the kernel needs to be small, efficient, and loaded into a protected area in the memory so that it cannot be overwritten. It may be responsible for such essential tasks as disk drive management, file management, memory management, process management, etc.
L
library (computing)
A collection of non-volatile resources used by computer programs, often for software development. These may include configuration data, documentation, help data, message templates, pre-written code and subroutines, classes, values, or type specifications.
linear search
Also sequential search.
A method for finding an element within a list. It sequentially checks each element of the list until a match is found or the whole list has been searched.[138]
linked list
A linear collection of data elements, whose order is not given by their physical placement in memory. Instead, each element points to the next. It is a data structure consisting of a collection of nodes which together represent a sequence.
linker
or link editor, is a computer utility program that takes one or more object files generated by a compiler or an assembler and combines them into a single executable file, library file, or another 'object' file. A simpler version that writes its output directly to memory is called the loader, though loading is typically considered a separate process.[139]
list
An abstract data type that represents a countable number of ordered values, where the same value may occur more than once. An instance of a list is a computer representation of the mathematical concept of a finite sequence; the (potentially) infinite analog of a list is a stream.[140]:§3.5 Lists are a basic example of containers, as they contain other values. If the same value occurs multiple times, each occurrence is considered a distinct item.
loader
The part of an operating system that is responsible for loading programs and libraries. It is one of the essential stages in the process of starting a program, as it places programs into memory and prepares them for execution. Loading a program involves reading the contents of the executable file containing the program instructions into memory, and then carrying out other required preparatory tasks to prepare the executable for running. Once loading is complete, the operating system starts the program by passing control to the loaded program code.
logic error
In computer programming, a bug in a program that causes it to operate incorrectly, but not to terminate abnormally (or crash). A logic error produces unintended or undesired output or other behaviour, although it may not immediately be recognized as such.
logic programming
A type of programming paradigm which is largely based on formal logic. Any program written in a logic programming language is a set of sentences in logical form, expressing facts and rules about some problem domain. Major logic programming language families include Prolog, answer set programming (ASP), and Datalog.
M
machine learning (ML)
The scientific study of algorithms and statistical models that computer systems use to perform a specific task without using explicit instructions, relying on patterns and inference instead. It is seen as a subset of artificial intelligence. Machine learning algorithms build a mathematical model based on sample data, known as "training data", in order to make predictions or decisions without being explicitly programmed to perform the task.[141][142]
machine vision (MV)
The technology and methods used to provide imaging-based automatic inspection and analysis for such applications as automatic inspection, process control, and robot guidance, usually in industry. Machine vision refers to many technologies, software and hardware products, integrated systems, actions, methods and expertise. Machine vision as a systems engineering discipline can be considered distinct from computer vision, a form of computer science. It attempts to integrate existing technologies in new ways and apply them to solve real world problems. The term is the prevalent one for these functions in industrial automation environments but is also used for these functions in other environments such as security and vehicle guidance.
mathematical logic
A subfield of mathematics exploring the applications of formal logic to mathematics. It bears close connections to metamathematics, the foundations of mathematics, and theoretical computer science.[143] The unifying themes in mathematical logic include the study of the expressive power of formal systems and the deductive power of formal proof systems.
matrix
In mathematics, a matrix, (plural matrices), is a rectangular array[144] (see irregular matrix) of numbers, symbols, or expressions, arranged in rows and columns.[145][146]
memory
Computer data storage, often called storage, is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers.[147]:15–16
merge sort
Also mergesort.
An efficient, general-purpose, comparison-based sorting algorithm. Most implementations produce a stable sort, which means that the order of equal elements is the same in the input and output. Merge sort is a divide and conquer algorithm that was invented by John von Neumann in 1945.[148] A detailed description and analysis of bottom-up mergesort appeared in a report by Goldstine and von Neumann as early as 1948.[149]
method
In object-oriented programming (OOP), a procedure associated with a message and an object. An object consists of data and behavior. The data and behavior comprise an interface, which specifies how the object may be utilized by any of various consumers[150] of the object.
methodology
In software engineering, a software development process is the process of dividing software development work into distinct phases to improve design, product management, and project management. It is also known as a software development life cycle (SDLC). The methodology may include the pre-definition of specific deliverables and artifacts that are created and completed by a project team to develop or maintain an application.[151]
modem
Portmanteau of modulator-demodulator.
A hardware device that converts data into a format suitable for a transmission medium so that it can be transmitted from one computer to another (historically along telephone wires). A modem modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded reliably to reproduce the original digital data. Modems can be used with almost any means of transmitting analog signals from light-emitting diodes to radio. A common type of modem is one that turns the digital data of a computer into modulated electrical signal for transmission over telephone lines and demodulated by another modem at the receiver side to recover the digital data.
N
natural language processing (NLP)
A subfield of linguistics, computer science, information engineering, and artificial intelligence concerned with the interactions between computers and human (natural) languages, in particular how to program computers to process and analyze large amounts of natural language data. Challenges in natural language processing frequently involve speech recognition, natural language understanding, and natural language generation.
node
Is a basic unit of a data structure, such as a linked list or tree data structure. Nodes contain data and also may link to other nodes. Links between nodes are often implemented by pointers.
number theory
A branch of pure mathematics devoted primarily to the study of the integers and integer-valued functions.
numerical analysis
The study of algorithms that use numerical approximation (as opposed to symbolic manipulations) for the problems of mathematical analysis (as distinguished from discrete mathematics).
numerical method
In numerical analysis, a numerical method is a mathematical tool designed to solve numerical problems. The implementation of a numerical method with an appropriate convergence check in a programming language is called a numerical algorithm.
O
object
An object can be a variable, a data structure, a function, or a method, and as such, is a value in memory referenced by an identifier. In the class-based object-oriented programming paradigm, object refers to a particular instance of a class, where the object can be a combination of variables, functions, and data structures. In relational database management, an object can be a table or column, or an association between data and a database entity (such as relating a person's age to a specific person).[152]
object code
Also object module.
The product of a compiler.[153] In a general sense object code is a sequence of statements or instructions in a computer language,[154] usually a machine code language (i.e., binary) or an intermediate language such as register transfer language (RTL). The term indicates that the code is the goal or result of the compiling process, with some early sources referring to source code as a "subject program."
object-oriented analysis and design (OOAD)
A technical approach for analyzing and designing an application, system, or business by applying object-oriented programming, as well as using visual modeling throughout the software development process to guide stakeholder communication and product quality.
object-oriented programming (OOP)
A programming paradigm based on the concept of "objects", which can contain data, in the form of fields (often known as attributes or properties), and code, in the form of procedures (often known as methods). A feature of objects is an object's procedures that can access and often modify the data fields of the object with which they are associated (objects have a notion of "this" or "self"). In OOP, computer programs are designed by making them out of objects that interact with one another.[155][156] OOP languages are diverse, but the most popular ones are class-based, meaning that objects are instances of classes, which also determine their types.
open-source software (OSS)
A type of computer software in which source code is released under a license in which the copyright holder grants users the rights to study, change, and distribute the software to anyone and for any purpose.[157] Open-source software may be developed in a collaborative public manner. Open-source software is a prominent example of open collaboration.[158]
operating system (OS)
System software that manages computer hardware, software resources, and provides common services for computer programs.
optical fiber
A flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair.[159] Optical fibers are used most often as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths (data rates) than electrical cables. Fibers are used instead of metal wires because signals travel along them with less loss; in addition, fibers are immune to electromagnetic interference, a problem from which metal wires suffer.[160]
P
pair programming
An agile software development technique in which two programmers work together at one workstation. One, the driver, writes code while the other, the observer or navigator,[161] reviews each line of code as it is typed in. The two programmers switch roles frequently.
parallel computing
A type of computation in which many calculations or the execution of processes are carried out simultaneously.[162] Large problems can often be divided into smaller ones, which can then be solved at the same time. There are several different forms of parallel computing: bit-level, instruction-level, data, and task parallelism.
parameter
Also formal argument.
In computer programming, a special kind of variable, used in a subroutine to refer to one of the pieces of data provided as input to the subroutine.[b] These pieces of data are the values[163][164][165] of the arguments (often called actual arguments or actual parameters) with which the subroutine is going to be called/invoked. An ordered list of parameters is usually included in the definition of a subroutine, so that, each time the subroutine is called, its arguments for that call are evaluated, and the resulting values can be assigned to the corresponding parameters.
peripheral
Any auxiliary or ancillary device connected to or integrated within a computer system and used to send information to or retrieve information from the computer. An input device sends data or instructions to the computer; an output device provides output from the computer to the user; and an input/output device performs both functions.
pointer
Is an object in many programming languages that stores a memory address. This can be that of another value located in computer memory, or in some cases, that of memory-mapped computer hardware. A pointer references a location in memory, and obtaining the value stored at that location is known as dereferencing the pointer. As an analogy, a page number in a book's index could be considered a pointer to the corresponding page; dereferencing such a pointer would be done by flipping to the page with the given page number and reading the text found on that page. The actual format and content of a pointer variable is dependent on the underlying computer architecture.
postcondition
In computer programming, a condition or predicate that must always be true just after the execution of some section of code or after an operation in a formal specification. Postconditions are sometimes tested using assertions within the code itself. Often, postconditions are simply included in the documentation of the affected section of code.
precondition
In computer programming, a condition or predicate that must always be true just prior to the execution of some section of code or before an operation in a formal specification. If a precondition is violated, the effect of the section of code becomes undefined and thus may or may not carry out its intended work. Security problems can arise due to incorrect preconditions.
primary storage
(Also known as main memory, internal memory or prime memory), often referred to simply as memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required. Any data actively operated on is also stored there in uniform manner.
primitive data type
priority queue
An abstract data type which is like a regular queue or stack data structure, but where additionally each element has a "priority" associated with it. In a priority queue, an element with high priority is served before an element with low priority. In some implementations, if two elements have the same priority, they are served according to the order in which they were enqueued, while in other implementations, ordering of elements with the same priority is undefined.
procedural programming
procedure
In computer programming, a subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed. Subroutines may be defined within programs, or separately in libraries that can be used by many programs. In different programming languages, a subroutine may be called a routine, subprogram, function, method, or procedure. Technically, these terms all have different definitions. The generic, umbrella term callable unit is sometimes used.[166]
program lifecycle phase
Program lifecycle phases are the stages a computer program undergoes, from initial creation to deployment and execution. The phases are edit time, compile time, link time, distribution time, installation time, load time, and run time.
programming language
A formal language, which comprises a set of instructions that produce various kinds of output. Programming languages are used in computer programming to implement algorithms.
programming language implementation
Is a system for executing computer programs. There are two general approaches to programming language implementation: interpretation and compilation.[167]
programming language theory
(PLT) is a branch of computer science that deals with the design, implementation, analysis, characterization, and classification of programming languages and of their individual features. It falls within the discipline of computer science, both depending on and affecting mathematics, software engineering, linguistics and even cognitive science. It has become a well-recognized branch of computer science, and an active research area, with results published in numerous journals dedicated to PLT, as well as in general computer science and engineering publications.
Prolog
Is a logic programming language associated with artificial intelligence and computational linguistics.[168][169][170] Prolog has its roots in first-order logic, a formal logic, and unlike many other programming languages, Prolog is intended primarily as a declarative programming language: the program logic is expressed in terms of relations, represented as facts and rules. A computation is initiated by running a query over these relations.[171]
Python
Is an interpreted, high-level and general-purpose programming language. Created by Guido van Rossum and first released in 1991, Python's design philosophy emphasizes code readability with its notable use of significant whitespace. Its language constructs and object-oriented approach aim to help programmers write clear, logical code for small and large-scale projects.[172]
Q
quantum computing
The use of quantum-mechanical phenomena such as superposition and entanglement to perform computation. A quantum computer is used to perform such computation, which can be implemented theoretically or physically.[173]:I-5
queue
A collection in which the entities in the collection are kept in order and the principal (or only) operations on the collection are the addition of entities to the rear terminal position, known as enqueue, and removal of entities from the front terminal position, known as dequeue.
quicksort
Also partition-exchange sort.
An efficient sorting algorithm which serves as a systematic method for placing the elements of a random access file or an array in order.
R
R programming language
R is a programming language and free software environment for statistical computing and graphics supported by the R Foundation for Statistical Computing.[174] The R language is widely used among statisticians and data miners for developing statistical software[175] and data analysis.[176]
radix
Also base.
In digital numeral systems, the number of unique digits, including the digit zero, used to represent numbers in a positional numeral system. For example, in the decimal/denary system (the most common system in use today) the radix (base number) is ten, because it uses the ten digits from 0 through 9, and all other numbers are uniquely specified by positional combinations of these ten base digits; in the binary system that is the standard in computing, the radix is two, because it uses only two digits, 0 and 1, to uniquely specify each number.
record
A record (also called a structure, struct, or compound data) is a basic data structure. Records in a database or spreadsheet are usually called "rows".[177][178][179][180]
recursion
Occurs when a thing is defined in terms of itself or of its type. Recursion is used in a variety of disciplines ranging from linguistics to logic. The most common application of recursion is in mathematics and computer science, where a function being defined is applied within its own definition. While this apparently defines an infinite number of instances (function values), it is often done in such a way that no infinite loop or infinite chain of references can occur.
reference
Is a value that enables a program to indirectly access a particular datum, such as a variable's value or a record, in the computer's memory or in some other storage device. The reference is said to refer to the datum, and accessing the datum is called dereferencing the reference.
reference counting
A programming technique of storing the number of references, pointers, or handles to a resource, such as an object, a block of memory, disk space, and others. In garbage collection algorithms, reference counts may be used to deallocate objects which are no longer needed.
relational database
Is a digital database based on the relational model of data, as proposed by E. F. Codd in 1970.[181] A software system used to maintain relational databases is a relational database management system (RDBMS). Many relational database systems have an option of using the SQL (Structured Query Language) for querying and maintaining the database.[182]
reliability engineering
A sub-discipline of systems engineering that emphasizes dependability in the lifecycle management of a product. Reliability describes the ability of a system or component to function under stated conditions for a specified period of time.[183] Reliability is closely related to availability, which is typically described as the ability of a component or system to function at a specified moment or interval of time.
regression testing
(rarely non-regression testing[184]) is re-running functional and non-functional tests to ensure that previously developed and tested software still performs after a change.[185] If not, that would be called a regression. Changes that may require regression testing include bug fixes, software enhancements, configuration changes, and even substitution of electronic components.[186] As regression test suites tend to grow with each found defect, test automation is frequently involved. Sometimes a change impact analysis is performed to determine an appropriate subset of tests (non-regression analysis[187]).
requirements analysis
In systems engineering and software engineering, requirements analysis focuses on the tasks that determine the needs or conditions to meet the new or altered product or project, taking account of the possibly conflicting requirements of the various stakeholders, analyzing, documenting, validating and managing software or system requirements.[188]
robotics
An interdisciplinary branch of engineering and science that includes mechanical engineering, electronic engineering, information engineering, computer science, and others. Robotics involves design, construction, operation, and use of robots, as well as computer systems for their perception, control, sensory feedback, and information processing. The goal of robotics is to design intelligent machines that can help and assist humans in their day-to-day lives and keep everyone safe.
round-off error
Also rounding error.[189]
The difference between the result produced by a given algorithm using exact arithmetic and the result produced by the same algorithm using finite-precision, rounded arithmetic.[190] Rounding errors are due to inexactness in the representation of real numbers and the arithmetic operations done with them. This is a form of quantization error.[191] When using approximation equations or algorithms, especially when using finitely many digits to represent real numbers (which in theory have infinitely many digits), one of the goals of numerical analysis is to estimate computation errors.[192] Computation errors, also called numerical errors, include both truncation errors and roundoff errors.[193]
router
A networking device that forwards data packets between computer networks. Routers perform the traffic directing functions on the Internet. Data sent through the internet, such as a web page or email, is in the form of data packets. A packet is typically forwarded from one router to another router through the networks that constitute an internetwork (e.g. the Internet) until it reaches its destination node.[194]
routing table
In computer networking a routing table, or routing information base (RIB), is a data table stored in a router or a network host that lists the routes to particular network destinations, and in some cases, metrics (distances) associated with those routes. The routing table contains information about the topology of the network immediately around it.
run time
Runtime, run time, or execution time is the final phase of a computer program's life cycle, in which the code is being executed on the computer's central processing unit (CPU) as machine code. In other words, "runtime" is the running phase of a program.
run time error
A runtime error is detected after or during the execution (running state) of a program, whereas a compile-time error is detected by the compiler before the program is ever executed. Type checking, register allocation, code generation, and code optimization are typically done at compile time, but may be done at runtime depending on the particular language and compiler. Many other runtime errors exist and are handled differently by different programming languages, such as division by zero errors, domain errors, array subscript out of bounds errors, arithmetic underflow errors, several types of underflow and overflow errors, and many other runtime errors generally considered as software bugs which may or may not be caught and handled by any particular computer language.
S
search algorithm
Any algorithm which solves the search problem, namely, to retrieve information stored within some data structure, or calculated in the search space of a problem domain, either with discrete or continuous values.
secondary storage
Also known as external memory or auxiliary storage, differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfer the desired data to primary storage. Secondary storage is non-volatile (retaining data when power is shut off). Modern computer systems typically have two orders of magnitude more secondary storage than primary storage because secondary storage is less expensive.
selection sort
Is an in-place comparison sorting algorithm. It has an O(n2) time complexity, which makes it inefficient on large lists, and generally performs worse than the similar insertion sort. Selection sort is noted for its simplicity and has performance advantages over more complicated algorithms in certain situations, particularly where auxiliary memory is limited.
semantics
In programming language theory, semantics is the field concerned with the rigorous mathematical study of the meaning of programming languages. It does so by evaluating the meaning of syntactically valid strings defined by a specific programming language, showing the computation involved. In such a case that the evaluation would be of syntactically invalid strings, the result would be non-computation. Semantics describes the processes a computer follows when executing a program in that specific language. This can be shown by describing the relationship between the input and output of a program, or an explanation of how the program will be executed on a certain platform, hence creating a model of computation.
sequence
In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order does matter. Like a set, it contains members (also called elements, or terms). The number of elements (possibly infinite) is called the length of the sequence. Unlike a set, the same elements can appear multiple times at different positions in a sequence, and order does matter. Formally, a sequence can be defined as a function whose domain is either the set of the natural numbers (for infinite sequences) or the set of the first n natural numbers (for a sequence of finite length n). The position of an element in a sequence is its rank or index; it is the natural number for which the element is the image. The first element has index 0 or 1, depending on the context or a specific convention. When a symbol is used to denote a sequence, the nth element of the sequence is denoted by this symbol with n as subscript; for example, the nth element of the Fibonacci sequence F is generally denoted Fn. For example, (M, A, R, Y) is a sequence of letters with the letter 'M' first and 'Y' last. This sequence differs from (A, R, M, Y). Also, the sequence (1, 1, 2, 3, 5, 8), which contains the number 1 at two different positions, is a valid sequence. Sequences can be finite, as in these examples, or infinite, such as the sequence of all even positive integers (2, 4, 6, ...). In computing and computer science, finite sequences are sometimes called strings, words or lists, the different names commonly corresponding to different ways to represent them in computer memory; infinite sequences are called streams. The empty sequence ( ) is included in most notions of sequence, but may be excluded depending on the context.
serializability
In concurrency control of databases,[195][196] transaction processing (transaction management), and various transactional applications (e.g., transactional memory[197] and software transactional memory), both centralized and distributed, a transaction schedule is serializable if its outcome (e.g., the resulting database state) is equal to the outcome of its transactions executed serially, i.e. without overlapping in time. Transactions are normally executed concurrently (they overlap), since this is the most efficient way. Serializability is the major correctness criterion for concurrent transactions' executions[citation needed]. It is considered the highest level of isolation between transactions, and plays an essential role in concurrency control. As such it is supported in all general purpose database systems. Strong strict two-phase locking (SS2PL) is a popular serializability mechanism utilized in most of the database systems (in various variants) since their early days in the 1970s.
serialization
Is the process of translating data structures or object state into a format that can be stored (for example, in a file or memory buffer) or transmitted (for example, across a network connection link) and reconstructed later (possibly in a different computer environment).[198] When the resulting series of bits is reread according to the serialization format, it can be used to create a semantically identical clone of the original object. For many complex objects, such as those that make extensive use of references, this process is not straightforward. Serialization of object-oriented objects does not include any of their associated methods with which they were previously linked. This process of serializing an object is also called marshalling an object in some situations.[3][4] The opposite operation, extracting a data structure from a series of bytes, is deserialization, (also called unserialization or unmarshalling).
service level agreement
(SLA), is a commitment between a service provider and a client. Particular aspects of the service – quality, availability, responsibilities – are agreed between the service provider and the service user.[199] The most common component of an SLA is that the services should be provided to the customer as agreed upon in the contract. As an example, Internet service providers and telcos will commonly include service level agreements within the terms of their contracts with customers to define the level(s) of service being sold in plain language terms. In this case the SLA will typically have a technical definition in mean time between failures (MTBF), mean time to repair or mean time to recovery (MTTR); identifying which party is responsible for reporting faults or paying fees; responsibility for various data rates; throughput; jitter; or similar measurable details.
set
Is an abstract data type that can store unique values, without any particular order. It is a computer implementation of the mathematical concept of a finite set. Unlike most other collection types, rather than retrieving a specific element from a set, one typically tests a value for membership in a set.
soft computing
software
Computer software, or simply software, is a collection of data or computer instructions that tell the computer how to work. This is in contrast to physical hardware, from which the system is built and actually performs the work. In computer science and software engineering, computer software is all information processed by computer systems, programs and data. Computer software includes computer programs, libraries and related non-executable data, such as online documentation or digital media. Computer hardware and software require each other and neither can be realistically used on its own.
software agent
Is a computer program that acts for a user or other program in a relationship of agency, which derives from the Latin agere (to do): an agreement to act on one's behalf. Such "action on behalf of" implies the authority to decide which, if any, action is appropriate.[200][201] Agents are colloquially known as bots, from robot. They may be embodied, as when execution is paired with a robot body, or as software such as a chatbot executing on a phone (e.g. Siri) or other computing device. Software agents may be autonomous or work together with other agents or people. Software agents interacting with people (e.g. chatbots, human-robot interaction environments) may possess human-like qualities such as natural language understanding and speech, personality or embody humanoid form (see Asimo).
software construction
Is a software engineering discipline. It is the detailed creation of working meaningful software through a combination of coding, verification, unit testing, integration testing, and debugging. It is linked to all the other software engineering disciplines, most strongly to software design and software testing.[202]
software deployment
Is all of the activities that make a software system available for use.[203]
software design
Is the process by which an agent creates a specification of a software artifact, intended to accomplish goals, using a set of primitive components and subject to constraints.[204] Software design may refer to either "all the activity involved in conceptualizing, framing, implementing, commissioning, and ultimately modifying complex systems" or "the activity following requirements specification and before programming, as ... [in] a stylized software engineering process."[205]
software development
Is the process of conceiving, specifying, designing, programming, documenting, testing, and bug fixing involved in creating and maintaining applications, frameworks, or other software components. Software development is a process of writing and maintaining the source code, but in a broader sense, it includes all that is involved between the conception of the desired software through to the final manifestation of the software, sometimes in a planned and structured process.[206] Therefore, software development may include research, new development, prototyping, modification, reuse, re-engineering, maintenance, or any other activities that result in software products.[207]
software development process
In software engineering, a software development process is the process of dividing software development work into distinct phases to improve design, product management, and project management. It is also known as a software development life cycle (SDLC). The methodology may include the pre-definition of specific deliverables and artifacts that are created and completed by a project team to develop or maintain an application.[208] Most modern development processes can be vaguely described as agile. Other methodologies include waterfall, prototyping, iterative and incremental development, spiral development, rapid application development, and extreme programming.
software engineering
Is the systematic application of engineering approaches to the development of software.[209][210][211] Software engineering is a computing discipline.[212]
software maintenance
In software engineering is the modification of a software product after delivery to correct faults, to improve performance or other attributes.[213]
software prototyping
Is the activity of creating prototypes of software applications, i.e., incomplete versions of the software program being developed. It is an activity that can occur in software development and is comparable to prototyping as known from other fields, such as mechanical engineering or manufacturing. A prototype typically simulates only a few aspects of, and may be completely different from, the final product.
software requirements specification
(SRS), is a description of a software system to be developed. The software requirements specification lays out functional and non-functional requirements, and it may include a set of use cases that describe user interactions that the software must provide to the user for perfect interaction.
software testing
Is an investigation conducted to provide stakeholders with information about the quality of the software product or service under test.[214] Software testing can also provide an objective, independent view of the software to allow the business to appreciate and understand the risks of software implementation. Test techniques include the process of executing a program or application with the intent of finding software bugs (errors or other defects), and verifying that the software product is fit for use.
sorting algorithm
Is an algorithm that puts elements of a list in a certain order. The most frequently used orders are numerical order and lexicographical order. Efficient sorting is important for optimizing the efficiency of other algorithms (such as search and merge algorithms) that require input data to be in sorted lists. Sorting is also often useful for canonicalizing data and for producing human-readable output. More formally, the output of any sorting algorithm must satisfy two conditions:
The output is in nondecreasing order (each element is no smaller than the previous element according to the desired total order);
The output is a permutation (a reordering, yet retaining all of the original elements) of the input.
Further, the input data is often stored in an array, which allows random access, rather than a list, which only allows sequential access; though many algorithms can be applied to either type of data after suitable modification.
source code
In computing, source code is any collection of code, with or without comments, written using[215] a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source code. The source code is often transformed by an assembler or compiler into binary machine code that can be executed by the computer. The machine code might then be stored for execution at a later time. Alternatively, source code may be interpreted and thus immediately executed.
spiral model
Is a risk-driven software development process model. Based on the unique risk patterns of a given project, the spiral model guides a team to adopt elements of one or more process models, such as incremental, waterfall, or evolutionary prototyping.
stack
Is an abstract data type that serves as a collection of elements, with two main principal operations:
push, which adds an element to the collection, and
pop, which removes the most recently added element that was not yet removed.
The order in which elements come off a stack gives rise to its alternative name, LIFO (last in, first out). Additionally, a peek operation may give access to the top without modifying the stack.[216] The name "stack" for this type of structure comes from the analogy to a set of physical items stacked on top of each other. This structure makes it easy to take an item off the top of the stack, while getting to an item deeper in the stack may require taking off multiple other items first.[217]
state
In information technology and computer science, a system is described as stateful if it is designed to remember preceding events or user interactions;[218] the remembered information is called the state of the system.
statement
In computer programming, a statement is a syntactic unit of an imperative programming language that expresses some action to be carried out.[219] A program written in such a language is formed by a sequence of one or more statements. A statement may have internal components (e.g., expressions).
storage
Computer data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers.[147]:15–16
stream
Is a sequence of data elements made available over time. A stream can be thought of as items on a conveyor belt being processed one at a time rather than in large batches.
string
In computer programming, a string is traditionally a sequence of characters, either as a literal constant or as some kind of variable. The latter may allow its elements to be mutated and the length changed, or it may be fixed (after creation). A string is generally considered as a data type and is often implemented as an array data structure of bytes (or words) that stores a sequence of elements, typically characters, using some character encoding. String may also denote more general arrays or other sequence (or list) data types and structures.
structured storage
A NoSQL (originally referring to "non-SQL" or "non-relational")[220] database provides a mechanism for storage and retrieval of data that is modeled in means other than the tabular relations used in relational databases. Such databases have existed since the late 1960s, but the name "NoSQL" was only coined in the early 21st century,[221] triggered by the needs of Web 2.0 companies.[222][223] NoSQL databases are increasingly used in big data and real-time web applications.[224] NoSQL systems are also sometimes called "Not only SQL" to emphasize that they may support SQL-like query languages or sit alongside SQL databases in polyglot-persistent architectures.[225][226]
subroutine
In computer programming, a subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed. Subroutines may be defined within programs, or separately in libraries that can be used by many programs. In different programming languages, a subroutine may be called a routine, subprogram, function, method, or procedure. Technically, these terms all have different definitions. The generic, umbrella term callable unit is sometimes used.[227]
symbolic computation
In mathematics and computer science,[228] computer algebra, also called symbolic computation or algebraic computation, is a scientific area that refers to the study and development of algorithms and software for manipulating mathematical expressions and other mathematical objects. Although computer algebra could be considered a subfield of scientific computing, they are generally considered as distinct fields because scientific computing is usually based on numerical computation with approximate floating point numbers, while symbolic computation emphasizes exact computation with expressions containing variables that have no given value and are manipulated as symbols.
syntax
The syntax of a computer language is the set of rules that defines the combinations of symbols that are considered to be correctly structured statements or expressions in that language. This applies both to programming languages, where the document represents source code, and to markup languages, where the document represents data.
syntax error
Is an error in the syntax of a sequence of characters or tokens that is intended to be written in compile-time. A program will not compile until all syntax errors are corrected. For interpreted languages, however, a syntax error may be detected during program execution, and an interpreter's error messages might not differentiate syntax errors from errors of other kinds. There is some disagreement as to just what errors are "syntax errors". For example, some would say that the use of an uninitialized variable's value in Java code is a syntax error, but many others would disagree[229][230] and would classify this as a (static) semantic error.
system console
The system console, computer console, root console, operator's console, or simply console is the text entry and display device for system administration messages, particularly those from the BIOS or boot loader, the kernel, from the init system and from the system logger. It is a physical device consisting of a keyboard and a screen, and traditionally is a text terminal, but may also be a graphical terminal. System consoles are generalized to computer terminals, which are abstracted respectively by virtual consoles and terminal emulators. Today communication with system consoles is generally done abstractly, via the standard streams (stdin, stdout, and stderr), but there may be system-specific interfaces, for example those used by the system kernel.
T
technical documentation
In engineering, any type of documentation that describes handling, functionality, and architecture of a technical product or a product under development or use.[231][232][233] The intended recipient for product technical documentation is both the (proficient) end user as well as the administrator/service or maintenance technician. In contrast to a mere "cookbook" manual, technical documentation aims at providing enough information for a user to understand inner and outer dependencies of the product at hand.
third-generation programming language
A third-generation programming language (3GL) is a high-level computer programming language that tends to be more machine-independent and programmer-friendly than the machine code of the first-generation and assembly languages of the second-generation, while having a less specific focus to the fourth and fifth generations.[234] Examples of common and historical third-generation programming languages are ALGOL, BASIC, C, COBOL, Fortran, Java, and Pascal.
top-down and bottom-up design
tree
A widely used abstract data type (ADT) that simulates a hierarchical tree structure, with a root value and subtrees of children with a parent node, represented as a set of linked nodes.
type theory
In mathematics, logic, and computer science, a type theory is any of a class of formal systems, some of which can serve as alternatives to set theory as a foundation for all mathematics. In type theory, every "term" has a "type" and operations are restricted to terms of a certain type.
U
upload
In computer networks, to send data to a remote system such as a server or another client so that the remote system can store a copy.[235] Contrast download.
Uniform Resource Locator (URL)
Colloquially web address.[236]
A reference to a web resource that specifies its location on a computer network and a mechanism for retrieving it. A URL is a specific type of Uniform Resource Identifier (URI),[237][238] although many people use the two terms interchangeably.[239][c] URLs occur most commonly to reference web pages (http), but are also used for file transfer (ftp), email (mailto), database access (JDBC), and many other applications.
user
Is a person who utilizes a computer or network service. Users of computer systems and software products generally lack the technical expertise required to fully understand how they work.[242] Power users use advanced features of programs, though they are not necessarily capable of computer programming and system administration.
user agent
Software (a software agent) that acts on behalf of a user, such as a web browser that "retrieves, renders and facilitates end user interaction with Web content".[243] An email reader is a mail user agent.
user interface (UI)
The space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine from the human end, whilst the machine simultaneously feeds back information that aids the operators' decision-making process. Examples of this broad concept of user interfaces include the interactive aspects of computer operating systems, hand tools, heavy machinery operator controls, and process controls. The design considerations applicable when creating user interfaces are related to or involve such disciplines as ergonomics and psychology.
user interface design
Also user interface engineering.
The design of user interfaces for machines and software, such as computers, home appliances, mobile devices, and other electronic devices, with the focus on maximizing usability and the user experience. The goal of user interface design is to make the user's interaction as simple and efficient as possible, in terms of accomplishing user goals (user-centered design).
V
variable
In computer programming, a variable, or scalar, is a storage location (identified by a memory address) paired with an associated symbolic name (an identifier), which contains some known or unknown quantity of information referred to as a value. The variable name is the usual way to reference the stored value, in addition to referring to the variable itself, depending on the context. This separation of name and content allows the name to be used independently of the exact information it represents. The identifier in computer source code can be bound to a value during run time, and the value of the variable may therefore change during the course of program execution.[244][245]
virtual machine (VM)
An emulation of a computer system. Virtual machines are based on computer architectures and attempt to provide the same functionality as a physical computer. Their implementations may involve specialized hardware, software, or a combination of both.
V-Model
A software development process that may be considered an extension of the waterfall model, and is an example of the more general V-model. Instead of moving down in a linear way, the process steps are bent upwards after the coding phase, to form the typical V shape. The V-Model demonstrates the relationships between each phase of the development life cycle and its associated phase of testing. The horizontal and vertical axes represent time or project completeness (left-to-right) and level of abstraction (coarsest-grain abstraction uppermost), respectively.[246]
W
waterfall model
A breakdown of project activities into linear sequential phases, where each phase depends on the deliverables of the previous one and corresponds to a specialisation of tasks. The approach is typical for certain areas of engineering design. In software development, it tends to be among the less iterative and flexible approaches, as progress flows in largely one direction ("downwards" like a waterfall) through the phases of conception, initiation, analysis, design, construction, testing, deployment and maintenance.
Waveform Audio File Format
Also WAVE or WAV due to its filename extension.
An audio file format standard, developed by Microsoft and IBM, for storing an audio bitstream on PCs. It is an application of the Resource Interchange File Format (RIFF) bitstream format method for storing data in "chunks", and thus is also close to the 8SVX and the AIFF format used on Amiga and Macintosh computers, respectively. It is the main format used on Microsoft Windows systems for raw and typically uncompressed audio. The usual bitstream encoding is the linear pulse-code modulation (LPCM) format.
web crawler
Also spider, spiderbot, or simply crawler.
An Internet bot that systematically browses the World Wide Web, typically for the purpose of Web indexing (web spidering).
Wi-Fi
A family of wireless networking technologies, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access. Wi‑Fi is a trademark of the non-profit Wi-Fi Alliance, which restricts the use of the term Wi-Fi Certified to products that successfully complete interoperability certification testing.[247][248][249]
X
XHTML
Abbreviaton of eXtensible HyperText Markup Language.
Part of the family of XML markup languages. It mirrors or extends versions of the widely used HyperText Markup Language (HTML), the language in which web pages are formulated.
0–9
401a Retirement Plan
401k Retirement Plan
A type of retirement plan which is sponsored by an employer and in which the employer may match a portion of the employee's contributions. Most contributions are tax-deferred until retirement withdraws occur.
403b Retirement Plan
457 Retirement Plan
A
absolute advantage
Also called resource cost advantage.
The ability of a party (whether an individual, firm, or country) to produce a greater quantity of a good, product, or service than competitors using the same amount of resources.
abandonment of the gold standard
The decision by a government to abandon a monetary system in which the standard economic unit of account is based on a fixed quantity of gold.
adaptive expectations
A hypothetical process by which people form expectations about what will happen in the future based on what has happened in the past.
aggregate demand (AD)
Also called domestic final demand (DFD) or effective demand.
The total demand for goods and services in an economy.[1] It specifies the amounts of goods and services that will be purchased at all possible price levels.[2] Aggregate demand can also be interpreted as the demand for the gross domestic product of a country. It is often called effective demand, though this term also has a distinct meaning.
aggregate supply (AS)
Also called domestic final supply (DFS).
The total supply of goods and services in an economy.
aggregation problem
The difficult problem of finding a valid way to treat an empirical or theoretical aggregate as if it reacted like a less-aggregated measure, say, about behavior of an individual agent as described in general microeconomic theory.[3]
agent
An actor or, more specifically, a decision maker in a model of some aspect of the economy.
agricultural economics
An applied field of economics concerned with the application of economic theory in optimizing the production and distribution of food.
allocative efficiency
A state of the economy in which production represents consumer preferences; in particular, every good or service is produced up to the point where the last unit provides a marginal benefit to consumers equal to the marginal cost of producing. In the single-price model, at the point of allocative efficiency, price is equal to marginal cost.[4][5]
antitrust law
Also called a competition law or anti-monopoly law.
Any law that promotes or seeks to maintain market competition by regulating anti-competitive conduct by companies.[6][7] Competition law is implemented through public and private enforcement.[8] It is also known as "antitrust law" in the United States for historical reasons and as "anti-monopoly law" in China[6] and Russia.
applied economics
The application of economic theory and econometrics in specific settings. As one of the two sets of fields of economics (the other being the core),[9] it is typically characterized by the application of the core, i.e. economic theory and econometrics, to address practical issues in a range of fields.
appropriate technology
A movement (and its manifestations) encompassing technological choice and application that is small-scale, decentralized, labor-intensive, energy-efficient, environmentally sound, and locally autonomous.[10]
arbitrage
The practice of taking advantage of a price difference between two or more markets by striking a combination of matching deals that capitalize upon the imbalance, with the profit being the difference between the market prices.
Arrow's impossibility theorem
Austrian School
A heterodox[11][12][13] school of economic thought that is based on methodological individualism—the concept that social phenomena result from the motivations and actions of individuals.[14][15][16]
autarky
The quality of being self-sufficient; the term is usually applied to political states or their economic systems. Autarky exists whenever an entity can survive or continue its activities without external assistance or international trade. If a self-sufficient economy also deliberately refuses all trade with the outside world, then it is called a closed economy.[17]
automatic stabilizer
A feature of the structure of modern government budgets, particularly income taxes and welfare spending, that acts to dampen fluctuations in real GDP.[18]
autonomous consumption
Also called exogenous consumption.
The consumption expenditure that occurs when income levels are zero. Such consumption is considered autonomous of income only when expenditure on these consumables does not vary with changes in income; generally, it may be required to fund necessities and debt obligations. If income levels are actually zero, this consumption counts as dissaving, because it is financed by borrowing or using up savings.
average cost
Also called unit cost.
A quantity equal to the total cost divided by the number of goods produced (the output quantity, Q). It is also equal to the sum of variable costs (total variable costs divided by Q) plus average fixed costs (total fixed costs divided by Q).
average fixed cost
The fixed costs (FC) of production divided by the quantity (Q) of output produced. Fixed costs are those costs that must be incurred in fixed quantity regardless of the level of output produced.
average variable cost
A firm's variable costs (labour, electricity, etc.) divided by the quantity of output produced. Variable costs are those costs which vary with the output.
average tax rate
The ratio of the total amount of taxes paid to the total tax base (taxable income or spending), expressed as a percentage.[19]
B
backward induction
The process of reasoning backwards in time, from the end of a problem or situation, to determine a sequence of optimal actions. It proceeds by first considering the last time a decision might be made and choosing what to do in any situation at that time. Using this information, one can then determine what to do at the second-to-last time of decision. This process continues backwards until one has determined the best action for every possible situation (i.e. for every possible information set) at every point in time.
balance of payments
Also called balance of international payments and abbreviated B.O.P. or BoP.
A record or summary of all economic transactions between the residents of a country and the rest of the world in a particular period of time (e.g. over a quarter of a year or, more commonly, over a year). These transactions are made by individuals, firms and government bodies. Thus the balance of payments includes all external visible and non-visible transactions of a country.
balance of trade
Also called commercial balance or net exports (NX).
The difference between the monetary value of a nation's exports and imports over a certain period.[20] Sometimes a distinction is made between a balance of trade for goods versus one for services. "Balance of trade" can be a misleading term because trade measures a flow of exports and imports over a given period of time, rather than a balance of exports and imports at a given point in time. Also, balance of trade does not necessarily imply that exports and imports are "in balance" with each other or anything else.
balanced budget
A budget, particularly that of a government, in which revenues are equal to expenditures. Thus, neither a budget deficit nor a budget surplus exists (the accounts "balance"). The term may also refer more generally to a budget that has no budget deficit but could possibly have a budget surplus.[21] A cyclically balanced budget is a budget that is not necessarily balanced year-to-year, but is balanced over the economic cycle, running a surplus in boom years and running a deficit in lean years, with these offsetting over time.
bank
A financial institution that accepts deposits from the public and creates credit.[22] Lending activities can be performed either directly or indirectly through capital markets. Due to their importance in the financial stability of a country, banks are highly regulated in most countries. Most nations have institutionalized a system known as fractional reserve banking, under which banks hold liquid assets equal to only a portion of their current liabilities. In addition to other regulations intended to ensure liquidity, banks are generally subject to minimum capital requirements based on an international set of capital standards, known as the Basel Accords.
bankruptcy
The inability to pay debt due to loss of income, increased spending, or an unforeseen financial crisis.
barriers to entry
In theories of competition in economics, a cost that must be incurred by a new entrant into a market that incumbents do not have or have not had to incur.[23][24] Because barriers to entry protect incumbent firms and restrict competition in a market, they can contribute to distortionary prices and are therefore most important when discussing antitrust policy. Barriers to entry often cause or aid the existence of monopolies or give companies market power.
barter
In trade, a system of exchange in which participants in a transaction directly exchange goods or services for other goods or services without using a medium of exchange, such as money.[25] Economists distinguish barter from gift economies in many ways; barter, for example, features immediate reciprocal exchange that is not delayed in time. Barter usually takes place on a bilateral basis, but may be multilateral (i.e. mediated through a trade exchange). In most developed countries, barter usually only exists parallel to monetary systems to a very limited extent. Market actors use barter as a replacement for money as the method of exchange in times of monetary crisis, such as when currency becomes unstable (e.g. by hyperinflation or a deflationary spiral) or simply unavailable for conducting commerce.
behavioral economics
The branch of economics that studies the effects of psychological, cognitive, emotional, cultural and social factors on the economic decisions of individuals and institutions and how those decisions vary from those implied by classical theory.[26]
Bellman equation
bequest motive
Seeks to provide an economic justification for the phenomenon of intergenerational transfers of wealth; in other words, to explain why people leave money behind when they die.
Bertrand–Edgeworth model
A microeconomic model of price-setting oligopoly which studies what happens when there is a homogeneous product (i.e. consumers want to buy from the cheapest seller) where there is a limit to the output of firms which they are willing and able to sell at a particular price. This differs from the Bertrand competition model where it is assumed that firms are willing and able to meet all demand. The limit to output can be considered a physical capacity constraint which is the same at all prices (as in Edgeworth’s work) or to vary with price under other assumptions.
Black–Scholes model
Also called the Black–Scholes–Merton model.
A mathematical model for the dynamics of a financial market containing derivative investment instruments. From the partial differential equation in the model, known as the Black–Scholes equation, one can deduce the Black–Scholes formula, which gives a theoretical estimate of the price of European-style options and shows that the option has a unique price regardless of the risk of the security and its expected return (instead replacing the security's expected return with the risk-neutral rate). The formula led to a boom in options trading and provided mathematical legitimacy to the activities of the Chicago Board Options Exchange and other options markets around the world.[27] It is widely used, although often with adjustments and corrections, by options market participants.[28]:751
board of governors
The main governing body that directs the operations of the United States Federal Reserve System. Its seven members supervise the 12 Federal Reserve Districts.
bond
In finance, an instrument of indebtedness of the bond issuer to the holders. The most common types of bonds include municipal bonds and corporate bonds. The bond is a debt security, under which the issuer owes the holders a debt and (depending on the terms of the bond) is obliged to pay them interest (the coupon) or to repay the principal at a later date, termed the maturity date.[29] Interest is usually payable at fixed intervals (semiannual, annual, or sometimes monthly). Very often the bond is negotiable, that is, the ownership of the instrument can be transferred in the secondary market. This means that once the transfer agents at the bank medallion stamp the bond, it is highly liquid on the secondary market.[30]
borrower
See debtor.
break-even
Also called the break-even point (BEP).
The point at which total cost and total revenue are equal, i.e. "even". There is no net loss or gain, and one has "broken even", though opportunity costs have been paid and capital has received the risk-adjusted, expected return. In short, all costs that must be paid are paid, and there is neither profit nor loss.[31][32]
Bretton Woods system
A monetary system which established the rules for commercial and financial relations among the United States, Canada, Western Europe, Australia, and Japan after the 1944 Bretton Woods Agreement. The Bretton Woods system was the first example of a fully negotiated monetary order intended to govern monetary relations among independent states. The chief features were an obligation for each country to adopt a monetary policy that maintained its external exchange rates within 1 percent by tying its currency to gold and the ability of the IMF to bridge temporary imbalances of payments; there was also a need to address the lack of cooperation among other countries and to prevent competitive devaluation of the currencies.
budget deficit
Also simply called spending.
The amount by which spending exceeds revenue over a particular period of time; it is the opposite of budget surplus. The term may be applied to the budget of a government, private company, or individual.
budget set
Also called an opportunity set.
The set of all possible consumption bundles that an individual can afford, given the prices of goods and the individual's income level. The budget set is bounded above by the budget line. Graphically speaking, all the consumption bundles that lie inside and on the budget constraint form the budget set. By most definitions, budget sets must be compact and convex.
budget surplus
big push model
A concept in development economics or welfare economics that emphasizes that a firm's decision whether to industrialize or not depends on its expectation of what other firms will do. It assumes economies of scale and oligopolistic market structure and explains when industrialization would happen.
business cycle
Also called the economic cycle or trade cycle.
The downward and upward movement of gross domestic product (GDP) around its long-term growth trend.[33] The length of a business cycle is the period of time containing a single boom and contraction in sequence. These fluctuations typically involve shifts over time between periods of relatively rapid economic growth (expansions or booms) and periods of relative stagnation or decline (contractions or recessions).
business economics
A branch of applied economics which uses economic theory and quantitative methods to analyze business enterprises and the factors contributing to the diversity of organizational structures and the relationships of firms with labour, capital and product markets.[34]
business sector
Also called the corporate sector or sometimes simply business.
The part of the economy made up by companies.[35] It is generally considered a subset of the domestic economy,[36] excluding the economic activities of general government, of private households, and of non-profit organizations serving individuals.[37]
C
capacity utilization
The extent to which an enterprise or a nation uses its installed productive capacity. It is the relationship between output that is produced with the installed equipment and the potential output which could be produced with it if capacity was fully used.
capital
Any asset that can enhance one's power to perform economically useful work. Capital goods, real capital, or capital assets are already-produced, durable goods or any non-financial asset that is used in production of goods or services.[38] Capital is distinct from land (or non-renewable resources) in that capital can be increased by human labor. At any given moment in time, total physical capital may be referred to as the capital stock (which is not to be confused with the capital stock of a business entity).
capital cost
A fixed, one-time expense incurred on the purchase of land, buildings, construction, and equipment used in the production of goods or in the rendering of services. In other words, it is the total cost needed to bring a project to a commercially operable status. Whether a particular cost is capital or not depends on many factors, such as accounting, tax laws, and materiality.
capital flight
Occurs when money or assets rapidly flow out of a country due to an event of economic consequence. Such events may include an increase in taxes on capital or capital holders or the government of the country defaulting on its debt that disturbs investors and causes them to lower their valuation of the assets in that country or otherwise to lose confidence in its economic strength.
capital good
A durable good that is used in the production of goods or services. Capital goods are one of the three types of producer goods, the other two being land and labour, which are also known collectively as primary factors of production. This classification originated with classical economics and has remained the dominant method for classification.
cartel
Any group of firms that colludes and acts as a single coordinated whole to restrict output and drive up prices.
central bank
Also called a reserve bank or monetary authority.
An institution that manages the currency, money supply, and interest rates of an entire state or nation. Central banks also usually oversee the commercial banking system of their respective countries. In contrast to a commercial bank, a central bank possesses a monopoly on increasing the monetary base in the state, and usually also prints the national currency,[39] which usually serves as the state's legal tender. Central banks also act as a "lender of last resort" to the banking sector during times of financial crisis. Most central banks usually also have supervisory and regulatory powers to ensure the solvency of member institutions, prevent bank runs, and prevent reckless or fraudulent behavior by member banks.
Certificate of Deposit (CD or COD)
A savings instrument that usually earns more interest than a savings account but is bound by limits set within a contract.
circular flow of income
Also simply called circular flow.
A model of the economy in which the major exchanges are represented as flows of money, goods and services, etc. between economic agents. The flows of money and goods exchanged in a closed circuit correspond in value, but run in the opposite direction. The circular flow analysis is the basis of national accounts and hence of macroeconomics.
circulation
classical economics
Or classical political economy, is a school of thought in economics that flourished, primarily in Britain, in the late 18th and early-to-mid 19th century. Its main thinkers are held to be Adam Smith, Jean-Baptiste Say, David Ricardo, Thomas Robert Malthus, and John Stuart Mill. These economists produced a theory of market economies as largely self-regulating systems, governed by natural laws of production and exchange (famously captured by Adam Smith's metaphor of the invisible hand).
command economy
An economy in which the government directs all economic activity.
commerce
Relates to "the exchange of goods and services, especially on a large scale".[40] It includes legal, economic, political, social, cultural and technological systems that operate in a country or in international trade.
commodity
an economic good or service that has full or substantial fungibility: that is, the market treats instances of the good as equivalent or nearly so with no regard to who produced them.[41]
comparative advantage
Also called opportunity cost advantage.
The ability to produce most efficiently given all of the other products that could be produced.
competition law
Also called an antitrust law or anti-monopoly law.
Any law that promotes or seeks to maintain market competition by regulating anti-competitive conduct by companies.[6][7]
competitive market
A market in which many sellers compete against each other to attract customers. Each seller has an incentive to sell at the lowest price possible to attract customers, so prices tend to be driven so low that the sellers can just barely make a profit.
complementary goods
Goods that are bought and used together.
compound interest
The addition of interest to the principal sum of a loan or deposit; it is often interpreted as "interest on interest". Compound interest is the result of reinvesting interest, rather than paying it out, so that interest in the next period is then earned on the principal sum plus any previously accumulated interest. Contrast simple interest.
computational economics
A research discipline at the interface of economics, computer science, and management science[42] which encompasses computational modeling of economic systems, whether agent-based,[43] general-equilibrium,[44] macroeconomic,[45] or rational-expectations,[46] computational econometrics and statistics,[47] computational finance, computational tools for the design of automated internet markets, programming tools specifically designed for computational economics, and pedagogical tools for the teaching of computational economics.
consumer
A member of a household that spends on goods and services.
consumer choice
A theory of microeconomics that relates preferences to consumption expenditures and to consumer demand curves. It analyzes how consumers maximize the desirability of their consumption as measured by their preferences subject to limitations on their expenditures, by maximizing utility subject to a consumer budget constraint.[48]
consumer confidence
An economic indicator that measures the degree of optimism that consumers feel about the overall state of the economy and their personal financial situation.
consumer price index (CPI)
Measures changes in the price level of market basket of consumer goods and services purchased by households. The CPI is a statistical estimate constructed using the prices of a sample of representative items whose prices are collected periodically. Sub-indices and sub-sub-indices are computed for different categories and sub-categories of goods and services, being combined to produce the overall index with weights reflecting their shares in the total of the consumer expenditures covered by the index. It is one of several price indices calculated by most national statistical agencies. The annual percentage change in a CPI is used as a measure of inflation. A CPI can be used to index (i.e. adjust for the effect of inflation) the real value of wages, salaries, and pensions; to regulate prices; and to deflate monetary magnitudes to show changes in real values. In most countries, the CPI, along with the population census, is one of the most closely watched national economic statistics.
consumer surplus
the difference between the maximum price a consumer is willing to pay and the actual price they do pay. If a consumer is willing to pay more for a unit of a good than the current asking price, they are getting more benefit from the purchased product than they would if the price was their maximum willingness to pay. They are receiving the same benefit, the obtainment of the good, with a smaller cost as they are spending less than they would if they were charged their maximum willingness to pay.[49]
consumerism
Economic policies which emphasize consumption.
consumption
According to mainstream economists, only the final purchase of goods and services by individuals constitutes consumption, while other types of expenditure — in particular, fixed investment, intermediate consumption, and government spending — are placed in separate categories (see consumer choice). Other economists define consumption much more broadly, as the aggregate of all economic activity that does not entail the design, production and marketing of goods and services (e.g. the selection, adoption, use, disposal and recycling of goods and services).
consumption function
A mathematical function which describes a relationship between consumption and disposable income.[50][51] The concept is believed to have been introduced into macroeconomics by John Maynard Keynes in 1936, who used it to develop the notion of a government spending multiplier.[52]
contract curve
In microeconomics, the contract curve is the set of points representing final allocations of two goods between two people that could occur as a result of mutually beneficial trading between those people given their initial allocations of the goods. All the points on this locus are Pareto efficient allocations, meaning that from any one of these points there is no reallocation that could make one of the people more satisfied with his or her allocation without making the other person less satisfied. The contract curve is the subset of the Pareto efficient points that could be reached by trading from the people's initial holdings of the two goods.
contract theory
The study of how economic actors can and do construct contractual arrangements, generally in the presence of asymmetric information. Because of its connections with both agency and incentives, contract theory is often categorized within a field known as law and economics.
convexity
In the Arrow–Debreu model of general economic equilibrium, agents have convex budget sets and convex preferences: at equilibrium prices, the budget hyperplane supports the best attainable indifference curve.[53] The profit function is the convex conjugate of the cost function.[54][55] Convex analysis is the standard tool for analyzing textbook economics.[54] Non‑convex phenomena in economics have been studied with nonsmooth analysis, which generalizes convex analysis.[56]
corporation
A type of business organization owned by many people but treated by law as though it were an individual person; it can own property, pay taxes, make contracts, and contribute to political causes.
cost
1. The value of money that is used up to produce a good or deliver a service, and hence is no longer available for further use. In business, the cost may be one of acquisition, in which case the amount of money expended to acquire a good or service is counted as the cost; in this case, money is the input that is gone in order to acquire the thing. This acquisition cost may be the sum of the cost of production as incurred by the original producer and of further costs of transaction as incurred by the acquirer over and above the price paid to the producer. Usually, the price designated by the producer also includes a mark-up for profit over the cost of production.
2. More generally, a performance metric that is totaling up as a result of a process or as a differential for the result of a decision.[57] Hence cost is the metric used in the standard modeling paradigm applied to economic processes. Costs (pl.) are often further described based on their timing or their applicability.
cost curve
A graph of the costs of production as a function of total quantity produced. In a free market economy, productively efficient firms optimize their production process by minimizing cost consistent with each possible level of production, and the result is a cost curve; and profit maximizing firms use cost curves to decide output quantities. There are various types of cost curves, all related to each other, including total and average cost curves; marginal ("for each additional unit") cost curves, which are equal to the differential of the total cost curves; and variable cost curves. Some are applicable to the short run, others to the long run.
cost of living
The cost of maintaining a certain standard of living. Changes in the cost of living over time are often operationalized in a cost-of-living index. Cost of living calculations are also used to compare the cost of maintaining a certain standard of living in different geographic areas. Differences in cost of living between locations can also be measured in terms of purchasing power parity rates.
cost overrun
Also called cost increase or budget overrun.
A situation involving unexpected incurred costs. A cost overrun occurs when an underestimation of the actual cost during budgeting results in costs that are in excess of budgeted amounts.
cost-benefit analysis (CBA)
Sometimes called benefit costs analysis (BCA).
A systematic approach to estimating the strengths and weaknesses of alternative options (for example in transactions, activities, or functional business requirements). It is often used to determine the option or options that provide the best approach to achieve benefits while preserving savings.[58] Cost-benefit analysis may be used to compare potential (or completed) courses of actions, or estimate (or evaluate) the value against costs of a single decision, project, or policy. Common areas of application include commercial transactions, functional business decisions, policy decisions (especially government policy), and project investments.
cost-of-production theory of value
The theory that the price of an object or condition is determined by the sum of the cost of the resources that went into producing it. The cost can comprise any of the factors of production (including labor, capital, or land) as well as taxation.
credit bureau
An agency that tracks the credit, employment, and housing history of consumers and assigns them a credit score.
credit card
A payment card issued to users (cardholders) to enable the cardholder to pay a merchant for goods and services based on the cardholder's promise to the card issuer to pay them at a later time for the cost of the good or service plus other agreed-upon fees and charges.[59] The card issuer (usually a bank) creates a revolving account and grants a line of credit to the cardholder, from which the cardholder can borrow money for payment to a merchant or as a cash advance.
credit score
A numerical value assigned to a person's potential ability to repay debt. A good credit score in the United States is approximately 700.
credit rating
An evaluation of the credit risk of a prospective debtor (an individual, business, company, or government), predicting their ability to pay back the debt, and an implicit forecast of the likelihood of the debtor defaulting on the debt.[60] Credit rating represents an evaluation of a credit rating agency of the qualitative and quantitative information for the prospective debtor, including information provided by the prospective debtor and other non-public information obtained by the credit rating agency's analysts. A subset of credit rating called credit reporting or credit score is a numeric evaluation of an individual's credit worthiness, which is conducted by a credit bureau or consumer credit reporting agency.
credit union
A financial institution that is usually local and owned by its members.
creditor
A person or a firm that lends money to a borrower.
crowding out
A phenomenon that occurs when increased government involvement in a sector of a market economy substantially affects the remainder of the market, either on the supply or demand side of the market.
cultural economics
The branch of economics that studies the relationship between culture and economic outcomes. Here, "culture" is defined by shared beliefs and preferences of respective groups. Programmatic issues include whether and how much culture matters to economic outcomes and what its relation is to institutions.[61] As a growing field in behavioral economics, the role of culture in economic behavior is increasingly being demonstrated to cause significant differentials in decision-making and the management and valuation of assets.
currency
Money in any form when in actual use or circulation as a medium of exchange, especially circulating banknotes and coins.[62][63] A more general definition is that a currency is a "system" of money (monetary units) in common use, especially within a particular nation.[64]
current account
A country's current account is one of the two components of its balance of payments, the other being the capital account (also known as the financial account). The current account consists of the balance of trade, net primary income or factor income (earnings on foreign investments minus payments made to foreign investors) and net cash transfers, that have taken place over a given period of time. The current account balance is one of two major measures of a country's foreign trade (the other being the net capital outflow). A current account surplus indicates that the value of a country's net foreign assets (i.e. assets less liabilities) grew over the period in question, and a current account deficit indicates that it shrank. Both government and private payments are included in the calculation. It is called the current account because goods and services are generally consumed in the current period.[65][66]
cyclical unemployment
Unemployment resulting from the business cycle. It is unpredictable.
D
deadweight loss
Also called excess burden or allocative inefficiency.
A loss of economic efficiency that occurs when the free-market equilibrium for a good or service is not achieved. Deadweight loss can be caused by monopoly pricing in the case of artificial scarcity, an externality, a tax or subsidy, or a compulsory price ceiling or price floor such as a minimum wage.
debt
Total money owed.
debtor
An entity that owes a debt to another entity. The entity may be an individual, a firm, a government, a company, or another legal person. The counterparty to which the debt is owed is called a creditor. When the counterparty of the arrangement is a bank, the debtor is more often referred to as a borrower.
deficit spending
Also called budget deficit or simply deficit.
The amount by which spending exceeds revenue over a particular period of time; it is the opposite of budget surplus. The term may be applied to the budget of a government, private company, or individual.
deflation
A decrease in the general price level of goods and services.[67] Deflation occurs when the inflation rate falls below 0% (a negative inflation rate); though inflation reduces the value of currency over time, deflation increases it. This allows more goods and services to be bought than before with the same amount of currency. Deflation is distinct from disinflation, which occurs when the inflation rate decreases but is still positive.[68]
deflator
A value that allows data to be measured over time in terms of some base period, usually through a price index, in order to distinguish between changes in the money value of a gross national product (GNP) that come from a change in prices, and changes from a change in physical output. It is the measure of the price level for some quantity. A deflator serves as a price index in which the effects of inflation are nulled.[69][70][71] It is the difference between real and nominal GDP.[72][73]
demand
The whole range of quantities that a person or group with a given income and preferences demands at various prices.
demand curve
A line on a graph that represents how much of a good or service buyers are going to consume at various prices.
demand deposit
Demand deposits, bank money or scriptural money are funds held in demand deposit accounts in commercial banks.[74] These account balances are usually considered money and form the greater part of the narrowly defined money supply of a country.[75]
demand shock
A sudden event that increases or decreases demand for goods or services temporarily.
demographic economics
Also called population economics.
The application of economic analysis to demography, the study of human populations, including size, growth, density, distribution, and vital statistics.[76][77]
depreciation
The gradual decrease in the economic value of the capital stock of a firm, nation, or other entity, either through physical depreciation, obsolescence, or changes in the demand for the services of the capital in question. If the capital stock is K t {\displaystyle K_{t}} K_{t} in one period t {\displaystyle t} t, gross (total) investment spending on newly produced capital is I t {\displaystyle I_{t}} I_t and depreciation is D t {\displaystyle D_{t}} D_{t}, the capital stock in the next period, K t + 1 {\displaystyle K_{t+1}} {\displaystyle K_{t+1}}, is K t + I t − D t {\displaystyle K_{t}+I_{t}-D_{t}} {\displaystyle K_{t}+I_{t}-D_{t}}. The net increment to the capital stock is the difference between gross investment and depreciation, and is called net investment.
depression
A sustained, long-term decrease in economic activity in one or more economies. It is a more severe economic downturn than a recession, which is a slowdown in economic activity over the course of a normal business cycle.
deregulation
The process of removing or reducing economic regulations, or the total repeal of governmental regulation of the economy. It became common in advanced industrial economies in the 1970s and 1980s, as a result of new trends in economic thinking about the inefficiencies of government regulation, and the risk that regulatory agencies would be controlled by the regulated industry to its benefit, and thereby hurt consumers and the wider economy.
diminishing marginal utility
A situation where each additional, or marginal, unit of a good or service that is consumed brings less utility than the previous unit.
diminishing returns
The decrease in the marginal (incremental) output of a production process as the amount of a single factor of production is incrementally increased, while the amounts of all other factors of production stay constant. The law of diminishing returns states that in all productive processes, adding more of one factor of production while holding all others constant ("ceteris paribus"), will at some point yield lower incremental per-unit returns.[78] It does not imply that adding more of a factor will decrease the total production, a condition known as negative returns, though in practice this is common.
discretionary income
Money available after one pays taxes.
disinflation
A decrease in the rate of inflation; a slowdown in the rate of increase of the general price level of goods and services in an economy's gross domestic product over time. It is the opposite of reflation. Disinflation is also distinct from deflation, which occurs when the inflation rate is negative.
disposable income
Money available after one pays taxes and obligatory bill payments.
dissaving
Negative saving, which occurs when spending is greater than disposable income. This spending may be financed by already accumulated savings, such as money in a savings account, or it can be borrowed.
distribution
The way total economic output, income, or wealth is distributed among individuals or among the factors of production (such as labor, land, and capital).[79] In general theory and the national income and product accounts, each unit of output corresponds to a unit of income.
domestic final demand (DFD)
See aggregate demand.
domestic final supply (DFS)
See aggregate supply.
duopoly
A situation in which there are exactly two suppliers for a particular good or service.
dynamic stochastic general equilibrium (DSGE)
Also abbreviated DGE and SDGE.
A method in macroeconomics that attempts to explain economic phenomena, such as economic growth and business cycles, and the effects of economic policy, through econometric models based on applied general equilibrium theory and microeconomic principles.
E
econometrics
The application of statistical methods to economic data in order to give empirical content to economic relationships.[80] More precisely, it is "the quantitative analysis of actual economic phenomena based on the concurrent development of theory and observation, related by appropriate methods of inference".[81]
economic costs
Total costs, including money spent on production and opportunity costs.
economic development
Broad improvement in the economic well-being or quality of life of a nation, region, or community, often but not necessarily as a consequence of economic growth.
economic efficiency
economic equilibrium
A situation in which economic forces such as supply and demand are balanced and in which, in the absence of external influences, the values of economic variables do not change. For example, in the standard textbook model of perfect competition, equilibrium occurs at the point at which quantity demanded and quantity supplied are equal.[82] Market equilibrium in this case is a condition in which a market price is established through competition such that the amount of goods or services sought by buyers is equal to the amount of goods or services produced by sellers. This price is often called the competitive price or market clearing price and will tend not to change unless demand or supply changes, and the quantity is called the "competitive quantity" or market clearing quantity. However, the concept of equilibrium in economics also applies to imperfectly competitive markets, where it takes the form of a Nash equilibrium.
economic growth
An increase in the inflation-adjusted market value of the goods and services produced by an economy over time. It is conventionally measured as the percent rate of increase in real gross domestic product, or real GDP.[83]
economic indicator
Any measurable unit of the economy which helps economists assess the past or make predictions about the future, such as unemployment rate and gross domestic product.
economic interdependence
The existence of necessary relationships between different sectors of the economy and how the decisions and actions of one will impact the others.
economic model
A theoretical construct representing an economic process by a set of variables and a set of logical and/or quantitative relationships between them. Economic models are usually simplified, often mathematical, frameworks designed to illustrate complex processes. Frequently, economic models posit structural parameters.[84] A model may have various exogenous variables, and those variables may change to create various responses by economic variables. Methodological uses of models include investigation, theorizing, and fitting theories to the world.[85]
economic profits
Also called economic rent.
Any monies collected by a firm above and beyond what is required to keep an entrepreneur owner interested in continuing in business.
economic rent
See economic profits.
economic shortage
Also called excess demand.
A situation in which the demand for a particular good or service exceeds its supply within a particular market. A shortage is the opposite of a surplus.
economic surplus
Also called excess supply.
A situation in which the supply of a good or service exceeds its demand within a particular market, often as a result of the current price being below the economic equilibrium.
economic system
Also called an economic order.[86]
A system of production, resource allocation, and distribution of goods and services within a society or a given geographic area. It includes the combination of the various institutions, agencies, entities, decision-making processes, and patterns of consumption that comprise the economic structure of a given community. As such, an economic system is a type of social system. The mode of production is a related concept.[87] All economic systems have three basic questions to ask: what to produce, how to produce it, and in what quantities and who receives the output of production.
economics
The social science that studies the production, distribution, and consumption of goods and services within economies.[88]
economies of agglomeration
economies of scale
The cost advantages that enterprises obtain as a result of the increased efficiency offered by a certain scale of operation (typically measured by amount of output produced), with cost per unit of output decreasing with increasing scale. At the basis of economies of scale there may be technical, statistical, organizational, or related factors to the degree of market control.
economies of scope
The cost advantages that enterprises obtain as a result of the increased efficiency offered by variety rather than by volume, with cost per unit of output decreasing with increasing variety.[89] In economics, "scope" is synonymous with broadening production through diversified products. For example, a gas station that sells gasoline can also sell soda, milk, baked goods, etc. through their customer service representatives, which may make the sale of gasoline more efficient.[90]
economist
A practitioner in the discipline of economics.
economy
An area of the production, distribution, trade, and consumption of goods and services by different agents. In its broadest sense, an economy may be defined as "a social domain that emphasizes the practices, discourses, and material expressions associated with the production, use, and management of resources".[91]
effective demand
elastic demand
Demand that is sensitive to changes in price, such that changes in price have a relatively large effect on the quantity of the good demanded. Contrast inelastic demand.
elasticity
The measurement of the proportional change of an economic variable in response to a change in another. Colloquially, elasticity is often interpreted as how easy it is for a supplier or consumer to change their behavior and substitute another good, the strength of an incentive over choices per the relative opportunity cost.
engineering economics
Previously known as engineering economy, is a subset of economics concerned with the use and "...application of economic principles"[92] in the analysis of engineering decisions.[93]
entrepreneurship
The efforts by a person, known as an entrepreneur, in organizing resources for the creation of something new or taking risks to create new innovations and production.
environmental economics
A sub-field of economics concerned particularly with environmental issues.
equal opportunity
A state of fairness in which job applicants are treated similarly, unhampered by artificial barriers or prejudices or preferences, except when particular distinctions can be explicitly justified.[94]
equilibrium
The point at which quantity demanded and quantity supplied are equal and both consumer and producer are satisfied.
equilibrium price
The market price at which both the supplier and consumer will trade and both are satisfied.
equity
Also called economic equality.
The concept or idea of fairness in economics, particularly in regard to taxation or welfare economics. More specifically, it may refer to equal life chances regardless of identity, to provide all citizens with a basic and equal minimum of income, goods, and services or to increase funds and commitment for redistribution.[95]
excess supply
Also called economic surplus.[96]
A situation in which the quantity of a good or service supplied is more than the quantity demanded,[97] and the price is above the equilibrium level determined by supply and demand; that is, the quantity of the product that producers wish to sell exceeds the quantity that potential buyers are willing to buy at the prevailing price. It is the opposite of an economic shortage.
exchange rate
The rate at which one currency is exchanged for another. It is also commonly regarded as the value of one country's currency relative to another currency.[98]
excludability
expected utility hypothesis
expeditionary economics
An emerging field of economic enquiry that focuses on the rebuilding and reconstructing of economies in post-conflict nations and providing support to disaster-struck nations. It focuses on the need for good economic planning on the part of developed nations to help prevent the creation of failed states. It also emphasizes the need for the structuring on new firms to rebuild national economies.[99]
experimental economics
externality
A cost or benefit that falls not on the person(s) directly involved in an activity, but on others. Externalities can be positive or negative.
F
factors of production
Inputs (resources) used to create goods and services, including land, labor, capital, and entrepreneurship.
federal funds rate target
Federal Open Market Committee (FOMC)
The twelve-member committee of the United States Federal Reserve that meets several times a year to decide the course of action that should be taken to control the money supply of the United States.
Federal Reserve System
Often simply the Federal Reserve or the Fed.
The central bank of the United States, created by Congress in 1913 and charged with the duty of regulating the money supply and monitoring its member banks.
finance
The study of money and how it is used. Specifically, it deals with the questions of how an individual, company, or government acquires the money needed – called capital in the company context – and how they then spend or invest that money.[100] Finance is often split into three areas: personal finance, corporate finance, and public finance.[101] At the same time, finance is about the overall "system",[101] i.e. the financial markets that allow the flow of money, via investments and other financial instruments, between and within these areas; this "flow" is facilitated by the financial services sector. A major focus within finance is thus investment management — called money management for individuals, and asset management for institutions — and finance then includes the associated activities of securities trading, investment banking, financial engineering, and risk management.
financial economics
financial institution
Any firm, such as a bank, that is in the business of holding money for those who save and lending money to those who need loans.
financial markets
Markets where people trade the property rights to assets (like real estate or stocks) or where savers lend money to borrowers.
financial planning
A series of steps used by a person or a firm to achieve a financial goal.
financial risk
The risk assumed by a saver or investor on future outcomes that involve financial losses and gains.
financial transaction
An agreement or communication carried out between a buyer and a seller to exchange an asset for payment.
fiscal policy
A government’s policy on taxes and spending.
fixed costs
Costs that have to be paid even if a firm is not producing anything.
foreign exchange market
Also called the currency market or abbreviated Forex or FX.
A global decentralized or over-the-counter market for the trading of currencies. This market determines the foreign exchange rate. It includes all aspects of buying, selling and exchanging currencies at current or determined prices. In terms of trading volume, it is by far the largest market in the world, followed by the credit market.[102]
free market
An economic system in which the prices for goods and services are self-regulated by the open market and by consumers. In a free market, the laws and forces of supply and demand are free from any intervention by a government or other authority and from all forms of economic privilege, monopolies, and artificial scarcities.[103] Proponents of the concept of the free market contrast it with a regulated market in which a government intervenes in supply and demand through various methods such as tariffs used to restrict trade and to protect the local economy. In an idealized free-market economy, prices for goods and services are set freely by the forces of supply and demand and are allowed to reach their point of equilibrium without intervention by government policy.
free trade
Trade between countries that occurs with few or no trade barriers.
frictional unemployment
Unemployment that is a result of workers moving from one job to another, as opposed to structural unemployment.
full employment
full employment output (Y*)
How much output is produced in the economy when full employment exists in the labor market.
functions of money
The four classic functions or uses of money as summarized by William Stanley Jevons in 1875: a medium of exchange, a common measure of value (or unit of account), a standard of value (or standard of deferred payment), and a store of value. This analysis later became a fundamental concept of macroeconomics. Most modern textbooks now list only three functions, that of medium of exchange, unit of account, and store of value, not considering a standard of deferred payment as a distinguished function, but rather subsuming it in the others.
future value
G
GDP deflator
general equilibrium theory
gift economy
good
government revenue
The total revenue received by all three levels of government (federal, state, and local) in the form of taxes and tariffs.
government spending
The total expenditure made by all three levels of government (federal, state, and local) for public services.
gross domestic product (GDP)
The value of all goods and services produced in the economy in a given period of time, usually a quarter or a year.
growth recession
A situation in which economic growth is slow but not low enough to be a recession, yet unemployment still increases.
[104]
H
health economics
heterodox economics
household
The sector of the economy which purchases goods from the product market and sells labor, land, and entrepreneurship ability to the factor market in the circular flow market.
housing starts
The number of new houses being built during a period of time.
human capital
The knowledge and skills that people use to help them produce output.
hyperinflation
Inflation which occurs at an extremely high rate, usually in excess of 20 or 30 per cent per month.
I
implicit cost
import quota
import
incentive
income
income distribution
income effect
The change in consumption resulting from a change in income.
increasing returns
A situation where each additional amount of a resource used in a production process brings forth successively larger amounts of output.
indifference curve
Individual Retirement Account (IRA)
A retirement (savings) instrument that allows a person to save money through time while deferring taxes on that income until retirement.
industrial organization
industry
A sector of the economy in which different firms produce similar or identical goods or services.
inelastic demand
Demand that is not very sensitive to changes in price, such that changes in price have a relatively small effect on the quantity of the good demanded. Contrast elastic demand.
inflation
When the overall level of prices in the economy is rising.
inflation rate
A measure of how the overall level of prices in the economy changes over time. If the inflation rate is positive, prices are rising; if the inflation rate is negative, prices are falling.
information economics
interest
interest rate
The price you have to pay to borrow money.
international economics
intertemporal choice
inventory bounce
investment
Any increase in the economy's stock of capital.
investment fund
invisible hand
Adam Smith’s famous idea that when constrained by competition, each firm’s greed causes it to act in a socially optimal way, as if guided to do the right thing by an invisible hand.
IS–LM model
J
JEL classification codes
job hunting
joint product pricing
just price
A theory of ethics which attempts to set standards of fairness for economic transactions.
K
Keynesian economics
Also called Keynesianism.
A diverse set of macroeconomic theories about how in the short run (and especially during recessions) economic output can be strongly influenced by the total amount of spending that occurs within an economy, known as aggregate demand. Keynesian economists generally argue that because aggregate demand is often unstable and behaves erratically, it does not necessarily or predictably equal the aggregate supply, which can cause market economies to experience inefficient macroeconomic outcomes in the form of recessions (when demand is low) and inflation (when demand is high), and that these outcomes can be mitigated by monetary policy actions by a central bank and fiscal policy actions by a government authority, which can help stabilize output over the business cycle.
L
labor
labor economics
laissez-faire
Law of Demand
An economic rule stating that quantity demanded and price move in opposite directions, i.e. as demand increases, price decreases, and vice versa.
Law of Diminishing Marginal Utility
An economic rule stating that the additional satisfaction a consumer gets from purchasing one more unit of a product will decrease with each additional unit purchased.
law of increasing costs
law of supply
lease
lending
leprechaun economics
Distortion of national accounts data by corporate tax schemes.
liability
Financial responsibility for something.
loan
local tax
Any tax paid to a city or county, e.g. sales taxes, school taxes, or property taxes.
long run
long-run shutdown condition
A situation where a firm’s total revenues exceed its variable costs but are less than its total costs. The firm continues to operate until its fixed cost contracts expire.
long-term financing
loose money policy
A monetary policy that makes credit inexpensive and abundant, possibly leading to inflation.
M
macroeconomics
The study of the economy as a whole, concentrating on economy-wide factors such as interest rates, inflation, and unemployment. Macroeconomics also encompasses the study of economic growth and how governments use monetary and fiscal policy to try to moderate the harm caused by recessions.
major trading partner
In international trading, a country or group of countries with which one country trades more than with others.
managerial economics
marginal cost
The additional increase in total cost when one more unit of output is produced.
marginal product of labor
marginal propensity to consume
marginal revenue
The additional income earned from selling one more unit of a good; sometimes equal to price.
marginal utility
The change in total utility that results from consuming the next unit of a good or service. Marginal utility can be positive or negative.
marginal value
marginalism
market
market basket
A bundle of goods and services selected to measure inflation. Economists define a market basket, such as the Consumer Price Index, and then track how much money it takes to buy this basket from one period to the next.
market economy
An economy in which almost all economic activity happens in markets, with little or no interference by the government; often referred to as a laissez-faire ("leave alone") economic system.
market failures
Situations where markets deliver socially non-optimal outcomes. Two common causes of market failure are asymmetric information and public goods.
market structure
The structure of a market as a whole, taking into consideration two main factors: the number of firms in the market and whether goods offered are identical, similar, or differentiated.
market production
Term that economists use to capture what happens when one individual offers to make or sell something to another individual at a price agreeable to both.
market system
markets
Places where buyers and sellers come together to trade money for a good or service.
mercantilism
microeconomics
A branch of economics that studies individual people and individual businesses. For people, microeconomics studies how they behave when faced with decisions about where to spend their money or how to invest their savings. For businesses, it studies how profit-maximising firms behave individually, as well as when competing against each other in markets.
monetarism
A school of thought in monetary economics which emphasizes the role of governments in controlling the amount of money in circulation (the money supply). Monetarists assert that variations in the money supply have major influences on national output in the short run and on price levels over longer periods, and that the objectives of monetary policy are best met by targeting the growth rate of the money supply rather than by engaging in discretionary policy.
monetary economics
monetary policy
Using changes in the money supply to change interest rates in order to stimulate or slow down economic activity.
monetary system
money
Anything customarily used as a medium of exchange, a unit of accounting, and a store of value.
money supply
monopolistic competition
A situation in which many firms with slightly different products compete. Production costs are above what may be achieved by perfectly competitive firms, but society benefits from the product differentiation.
monopoly
A firm with no competitors in its industry. A monopoly firm produces less output, has higher costs, and sells its output for a higher price than it would if constrained by competition.
monopsony
mortgage
motivation
multiplier
mutual fund
N
Nash equilibrium
national tax
Any tax paid to a national or federal government, e.g. income tax, tariffs, and social security taxes.
national wealth
The total value of capital and private property that is owned within a country.
natural monopoly
An industry in which one large producer can produce output at a lower cost than many small producers. It undersells its rivals and ends up as the only firm surviving in its industry.
natural resource economics
need
Any good or service that is fundamentally necessary for survival, such as food, clothing, and shelter.
nominal interest rates
Interest rates that measure the returns to a loan in terms of money borrowed and money returned (as opposed to real interest rates).
nominal prices
Money prices, which can change over time due to inflation. (See also real prices.)
nominal wages
Wages measured in money. (See also real wages.)
non-convexity
non-price determinant of demand
Any reason other than price that changes the will to buy a good or service, for example, fads, income, taste, future expectation, and population.
non-rivalry
O
oligopoly
An industry with only a few firms. If these firms collude, they form a cartel, which may reduce output and drive up profits in the same way a monopoly does.
oligopsony
open-market operations
The buying and selling of government bonds by a central bank; that is, transactions that take place in the public, or open, bond market.
opportunity cost
The value of the next best alternative thing that could have been done. It measures what is given up in order to do the most preferred thing.
organizational economics
P
Pareto efficiency
Also called Pareto optimality.
participation
partnership
A business that two or more individuals own and operate together.
per capita
A unit of account per person, usually placed at the end of an economic indicator.
perfect competition
A situation where numerous small firms producing identical products compete against each other in a given industry. Perfect competition leads to firms producing the socially optimal output level at the minimum possible cost per unit.
personal property
Possessions such as jewelry, furniture, and real estate that people can amass through time.
physical capital
All human-made goods that are used to produce other goods and services, such as tools, machines, and buildings.
physiocracy
population economics
See demographic economics.
preference
price
The amount of money it takes to buy a product or produce a product.
price ceiling
A market intervention in which the government ensures that the price of a good or service stays below the free market price.
price controls
price elasticity of demand
price elasticity of supply
price floor
A market intervention in which the government keeps the price of a good or service above its free-market price.
price index
A normalized average of price relatives for a given class of goods or services in a given region and during a given period of time. It is a statistic designed to help to compare how these price relatives, taken as a whole, differ between geographical locations or time periods. Notable price indices include consumer price index, producer price index, and GDP deflator.
price level
pricing
prime rate
Also called the prime lending rate.
The interest rate at which a bank will agree to lend to customers with good credit. Floating interest rates are often expressed as a percentage above or below the prime rate.
producer
An entity, either a person or firm, which supplies goods or services.
producer price index
producer surplus
The gain that producers receive when they can sell their output at a price higher than the minimum amount for which they are willing to make it.
product differentiation
production
production possibilities curve
A graph showing the maximal combinations of goods and services that can be produced from a fixed amount of resources in a given period of time.
productive efficiency
A term describing firms that produce goods and services at the lowest possible cost.
production set
profit
profit motive
progressive tax
A tax schedule that states that the more income one earns, the higher the tax rate will be.
proportional tax
Also called a flat tax.
A tax schedule that states that regardless of income, the same tax rate will be applied to all income earners.
proxemics
public economics
Or economics of the public sector, is the study of government policy through the lens of economic efficiency and equity. Public economics builds on the theory of welfare economics and is ultimately used as a tool to improve social welfare.
public good
Goods or services that cannot be profitably produced by private firms because they are impossible to provide to just one person; if you provide them to one person, you have to provide them to everybody. Public goods non-excludable (you can’t prevent anyone from consuming them) and non-rival (it costs no extra to supply one extra person).
pure competition
purchasing power parity (PPP)
Q
quantitative easing (QE)
quantity demanded
The amount of a good or service that a consumer is able and willing to purchase at a given price based on their income and preferences.
quantity supplied
The amount of a good or service that a supplier is able and willing to produce at a given market price.
quantity theory of money
The theory that the overall level of prices in the economy is proportional to the quantity of money circulating in the economy.
quota
A limited quantity of a product that can be produced, imported, or exported.
R
rate of profit
rational choice
The idea of making choices by using logic and that people will choose the most beneficial of the options afforded.
rational expectations
The theory that people optimally change their behaviour in response to policy changes. Depending on the situation, their behavioural changes can greatly limit the effectiveness of policy changes.
rationing
real income effect
The change in consumption resulting from a change in income, adjusted for inflation.
real interest rates
Interest rates that compensate for inflation by measuring the returns to a loan in terms of units of stuff lent and units of stuff returned (as opposed to nominal interest rates).
real GDP
Gross domestic product that has been adjusted for inflation by applying the price deflator.
real prices
How much of one kind of thing (such as hours worked) you have to give up to get a good or service, no matter what happens to nominal prices.
real wages
Wages measured not in terms of money itself (as nominal wages are) but rather in terms of how much output that money can buy.
recessions
Part of the business cycle during which an economy's total output falls.
recoveries
Part of the business cycle during which an economy’s total output expands.
reflation
regional science
regressive tax
A tax schedule that states that the more income one earns, the lower the tax burden.
regulation
Government restrictions on a business firm.
retail sales
Purchases of finished goods and services by households and firms.
returns to scale
revenue
Total income from sales of output.
rights
right to work law
A state law forbidding labor unions from forcing workers to join and pay union dues.
risk aversion
risk-return relationship
The direct relationship between the risk of an investment and its expected return or profit; the higher the risk, the higher the opportunity for gain or loss and vice versa.
rivalry
S
saving
scarcity
Any situation in which people do not have enough resources to satisfy all of their wants. The phenomenon of scarcity is what creates the need for economics.
sector
A portion or component of the larger economy, such as households, firms, or the government.
service
service economy
shift work
short run
shortage
short-run shutdown condition
A situation in which a firm’s total revenues are less than its variable costs, and the firm is better off shutting down immediately and losing only its fixed costs.
shrinkflation
social behavior
social choice theory
social mobility
socialist economics
sociality
socially optimal output level
The output level that maximises the benefits that society can get from its limited supply of resources.
socioeconomics
Also called social economics.
sole proprietorship
A business owned and operated by one person.
stagflation
A simultaneous economic phenomenon during which inflation and unemployment are both rising.
standard of living
state tax
Any tax paid to a state government, e.g. sales taxes, state income tax, and license plate fees.
sticky prices
Prices that are slow to adjust to shocks. Price stickiness can cause recessions to linger.
Stockholm School
structural unemployment
Unemployment created due to a decrease in demand for the skills of a worker.
substitution effect
When consumers react to an increase in a good's price by consuming less of that good and more of other goods.
substitute good
A product that can satisfy the utility of another.
sunk costs
supply
The total amount of a certain type of good that has been produced and is available.
supply and demand
An economic model of markets that separates buyers from sellers and then summarises each group’s behaviour with a single line on a graph. The buyers’ behaviour is captured by the demand curve, whereas the sellers’ behaviour is captured by the supply curve. By putting these two curves on the same graph, economists can show how buyers and sellers interact in markets to determine how much of any particular item is going to be sold, as well as the price at which it is likely to be sold.
supply chain
supply curve
A line on a graph that represents how much of a good or service sellers are going to produce at various prices.
supply schedule
A chart that lists how much of a good a supplier will offer at different prices.
supply shock
A sudden shortage of a good.
supply-side economics
surplus
T
tariff
tax
tax rate
terms of trade
The rules that countries impose on each other in order to trade with each other.
theory of the firm
thermoeconomics
time value of money
total cost
total surplus
The sum of producer surplus and consumer surplus.
trade
traditional economy
An economy in which production and distribution are handled along the lines of long-standing cultural traditions.
transaction cost
a cost in making any economic trade when participating in a market.[105]
transport economics
trough
U
underemployment
Working at a job for which one is overqualified, or working part-time when full-time work is desired.
unemployment
Under-utilization of any factor of production, most commonly referring to labor.
unit of account
unitary elastic
unskilled labor
Labor that requires no specialized skills, education, or training to perform.
urban economics
utilitarianism
utility
The usefulness of a good or service in satisfying a need or a want.
V
value
value-added tax (VAT)
variable costs
Any cost that changes in proportion to the amount of goods or services that a firm produces.[106] Variable costs are also the sum of marginal costs over all units produced.
velocity of money
Also called the velocity of circulation of money.
Refers to how fast money passes from one holder to the next. It can refer to the income velocity of money, which is the frequency with which the average same unit of currency is used to purchase newly domestically produced goods and services within a given time period.[107] In other words, it is the number of times one unit of money is spent to buy goods and services per unit time.[107]
W
wage
The monetary compensation (or remuneration, personnel expenses, labor) paid by an employer to an employee in exchange for work done. Payment is typically calculated as a fixed amount for each task completed (a task wage or piece rate), or at an hourly or daily rate (wage labour), or based on some other easily measured quantity of work done.
want
Wants are often distinguished from needs. A need is something that is necessary for survival (such as food and shelter), whereas a want is simply something that a person would like to have. Some economists have rejected this distinction and maintain that all of these are simply wants, with varying levels of importance. By this viewpoint, wants and needs can be understood as examples of the overall concept of demand.
wealth
The abundance of valuable financial assets or physical possessions which can be converted into a form that can be used for transactions. This includes the core meaning as held in the originating old English word weal, which is from an Indo-European word stem.[108] The modern concept of wealth is of significance in all areas of economics, especially for growth economics and development economics, yet the meaning of wealth is context-dependent. Individuals or companies possessing a substantial net worth are often referred to as wealthy. Net worth is defined as the current value of one's assets less liabilities (excluding the principal in trust accounts).[109]
wealth effect
The change in spending that accompanies a change in perceived wealth.[110] Usually the wealth effect is positive: spending changes in the same direction as perceived wealth.
welfare
A type of government support for the citizens of that society. Welfare may be provided to people of any income level, as with social security (and is then often called a social safety net), but it is usually intended to ensure that people can meet their basic human needs such as food and shelter. Welfare attempts to provide a minimal level of well-being, usually either a free- or a subsidized-supply of certain goods and social services, such as healthcare, education, and vocational training.[111]
welfare economics
A branch of economics that uses microeconomic techniques to evaluate well-being (welfare) at the aggregate (economy-wide) level.[112]
willingness to accept (WTA)
The minimum amount of money that а person is willing to accept to abandon a good or to put up with something negative, such as pollution. It is equivalent to the minimum monetary amount required for sale of a good or acquisition of something undesirable to be accepted by an individual.
willingness to pay (WTP)
The maximum price at or below which a consumer will definitely buy one unit of a product.[113] This corresponds to the standard economic view of a consumer reservation price. Some researchers, however, conceptualize WTP as a range.
Y
yield
In finance, the yield on a security is the amount of cash (in percentage terms) that returns to the owners of the security, in the form of interest or dividends received from it. Normally, it does not include the price variations, distinguishing it from the total return. Yield applies to various stated rates of return on stocks (common and preferred, and convertible), fixed income instruments (bonds, notes, bills, strips, zero coupon), and some other investment type insurance products (e.g. annuities).
Z
zero-sum game
In game theory and economic theory, a zero-sum game is a mathematical representation of a situation in which each participant's gain or loss of utility is exactly balanced by the losses or gains of the utility of the other participants. If the total gains of the participants are added up and the total losses are subtracted, they will sum to zero. Thus, cutting a cake, where taking a larger piece reduces the amount of cake available for others as much as it increases the amount available for that taker, is a zero-sum game if all participants value each unit of cake equally (see marginal utility).
A
abyssal plain
Flat or very gently sloping areas of the deep ocean basin floor.
absolute dating
The process of determining a specific date (in years or some other unit of time) for an archaeological, geological or paleontological site or artifact.
accident
A sudden discontinuity of ground, such as fault of great thickness, bed or lentil of unstable ground.[1]
accretion
A process by which material is added to a tectonic plate or landmass.
achnelith
A small, glassy volcanic bomb, sphere, dumbbell and droplet shapes resulting from very liquid magma.
acid rock
The groups ultrabasic, basic, intermediate and acid constitute a series with progressively increasing SiO2 content.
aftershock
A small earthquake that follows a main shock.
agglomerate
An indurated rock built of large angular rock fragments embedded in an ashy matrix and resulting from explosive volcanic activity. Occurs typically in volcanic vents.
aggregate
A mass consisting of rock or mineral fragments.
albite
The end member of the plagioclase group of minerals, ideally consisting of silicates of sodium and aluminium, but commonly containing small quantities of potash and lime in addition. Compare barbierite.
alkaline
A highly basic substance that dissolves in water.
alkaline rock
A type of rock characterized by a high content of Na2O and K2O relative to the other oxides. They occur throughout the range from ultrabasic to acid, but have their strongest expression in the acid-intermediate part of the range.
allochthon
A fossil, sediment, or rock that was formed elsewhere and later transported into the location where it is presently found, usually by low angle thrust faulting. An object of this type is referred to as allochthonous. Contrast autochthon.
alluvial fan
A fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain.
alluvium
Soil or sediments deposited by a river or other running water.
amber
Fossilized resin or tree sap that is appreciated for its vivid colour, usually reddish-orange to gold or yellow.
amphibole
An important group of dark-coloured, rock-forming silicate minerals, including hornblende, the commonest.
amphibolite
A crystalline, coarse-grained rock, containing amphibole as an essential constituent, together with feldspar and frequently garnet. Like hornblende schist, amphibolite is formed by regional metamorphism of basic igneous rocks, but is not foliated.
amygdaloidal
Amygdules or amygdales form when the gas bubbles or vesicles in volcanic lava (or other extrusive igneous rocks) are infilled with a secondary mineral such as calcite, quartz, chlorite or one of the zeolites. Rocks containing amygdules can be described as amygdaloidal.
anatexis
Melting of pre-existing rock. Compare metatexis, diatexis, and syntexis.
andalusite
One of several crystalline forms of aluminium silicate; a characteristic product if the contact metamorphism of argillaceous rocks.
andesite
Fine-grained igneous rock of intermediate composition. Up to half of the rock is plagioclase feldspar with the rest being ferromagnesian minerals.
angular unconformity
An unconformity in which younger strata overlie an erosion surface on tilted of folded layered rock.
anorthite
Also called Indianite.
A mineral from the lime-rich end of the plagioclase group of minerals. Anorthites are usually silicates of calcium and aluminium occurring in some basic igneous rocks, typically those produced by the contact metamorphism of impure calcareous sediments.
anticline
An arched fold in which the layers usually dip away from the fold axis. Contrast syncline.
aphanic
Having the texture of carbonate sedimentary rocks characterized by individual crystals or clastic grains less than 0.01 mm in diameter.
aphanitic
Said of the texture of igneous rock in which the crystalline components are not distinguishable by the naked eye. Both microcrystalline and cryptocrystalline textures are included.
aplogranite
A light-coloured rock of granitic texture consisting mainly of alkali feldspar and quartz, with subordinate biotite; muscovite may be present.
aquifer
A body of saturated rock or sediment through which water can move readily.
aragonite sea
Contains aragonite and high-magnesium calcite as the primary inorganic carbonate precipitates.
Archean Eon
The oldest eon of the Earth's history.
archipelago
A chain or cluster of islands.
arenaceous
Sediments consisting essentially of sand grains, that is, of quartz and rock fragments down to 0.005mm in size. Conglomerates, sandstones, grits and siltstones fall into this category Particle size 2mm to 1/16mm.
arenite
1. General term for consolidated sedimentary rock composed of sand sized fragments.
2. “Clean” sandstone, well-sorted, less than 10% argillaceous matrix. Opposite to Wacke.
arenitic
Pertaining to, having the quality of, or resembling sandstone.
arkose
An arenaceous sedimentary rock. Like sandstone in its general character but containing feldspar to at least 10%. Formed by the disintegration of the acid igneous rocks and gneisses.
argillaceous
Sedimentary rocks of the clay grade, i.e. composed of minute mineral fragments and crystals less than 0.005 mm in diameter, as well as large amounts of colloidal material. Apart from finely divided detrital matter, they consist of the so-called clay minerals, such as montmorillonite, kaolinite, gibbsite and diaspore. Siltstones, mudstones, shales, clays, etc. may all be referred to as argillaceous.
ash
Fragments less than 2 mm (0.079 in) in diameter of pulverized rock, minerals and volcanic glass, created during volcanic eruptions.
asphalt
A sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums and in some natural deposits.
assembled gem
Also called a composite gem.
asthenosphere
A region of the Earth's outer shell beneath the lithosphere. The asthenosphere is of indeterminate thickness and behaves plastically.
augite
A complex aluminous silicate of calcium, iron and magnesium, crystallising in the monoclinic system, and occurring in many igneous rocks, particularly those of basic composition. It is an essential component of basalt, dolerite and gabbro.
aureole
A zone surrounding an igneous intrusion in which country rock shows effects of contact metamorphism.
autochthon
A fossil, sediment, or rock that was formed or produced in the location where it is now found. The term is widely applied to a coal or peat that originated at the place where the plants comprising it grew and decayed and to rocks that have not been displaced by overthrust faulting. An object of this type is referred to as autochthonous. Contrast allochthon.
B
banded iron formation
A distinctive type of rock often found in primordial sedimentary rocks.
basalt
A fine-grained, mafic igneous rock composed predominantly of ferromagnesian minerals and with lesser amounts of calcium-rich plagioclase feldspar.
basement rock
The thick foundation of ancient, and oldest metamorphic and igneous rock that forms the crust of continents, often in the form of granite.
basic rock
Igneous rock with low silica content (<54%). The groups ultrabasic, basic, intermediate and acid constitute a series with progressively increasing SiO2 content.
basin
A landform scooped out by water erosion.
Basin and Range Province
A particular topography covering much of the southwestern United States and northwestern Mexico that is typified by elongate north-south trending arid valleys bounded by mountain ranges which also bound adjacent valleys.
batholith
A large discordant pluton with an outcropping area greater than 100 square kilometres (39 sq mi).
bedrock
Native consolidated rock underlying the loose rock or soil surface of the Earth.
Before Present (BP)
bioerosion
The erosion of hard ocean substrates by living organisms through various biological mechanisms.
biostratigraphy
A branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.
biostratinomy
The study of the processes that take place after an organism dies but before its final burial.
biotite
A form of black mica widely distributed in igneous rocks (particularly in granites) as lustrous black crystals, with a singularly perfect cleavage. In composition it is a complex silicate, chiefly of iron and magnesium, together with potassium and hydroxyl.
bioturbation
The displacement and mixing of sediment particles by benthic fauna (animals) or flora (plants).
blueschist
A rock that forms by the metamorphism of basalt or rocks of similar composition at high pressures and low temperatures, approximately corresponding to a depth of to and a temperature of to.
boudin
A structure formed by extension, in which a rigid tabular body such as a bed of sandstone is stretched and deformed amidst less competent beds. See also boudinage.
boulder
Bowen's reaction series
The sequence in which minerals crystallize from a cooling basaltic magma.
brackish
Water with a salinity higher than freshwater but lower than seawater.
breadcrust bomb
A rounded, smooth-surfaced volcanic bomb with a cracked surface resembling a cracked crust of bread, hence the name.
breccia
A coarse-grained clastic rock consisting largely of angular fragments of existing rocks.
buckling
A failure mode of a rock subjected to high compressive stresses, where the actual compressive stress at the point of failure is less than the ultimate compressive stresses that the material is capable of withstanding. Typically, folding is thought to occur by simple buckling of a planar surface and its confining volume. The volume change is accommodated by layer parallel shortening the volume, which grows in thickness.
C
calcareous
Formed from or containing a high proportion of calcium carbonate in the form of calcite or aragonite, used of a sediment, sedimentary rock, or soil type.
calcite
A mineral that is the crystalline form of calcium carbonate (CaCO3), showing trigonal symmetry and a great variety of mineral habits. It is one of the commonest of minerals in association with both igneous and sedimentary rocks.
calcite sea
A body of water in which low-magnesium calcite is the primary inorganic marine calcium carbonate precipitate.
calcrete
1. A conglomerate of surficial sand and gravel cemented by calcium carbonate precipitated from solution.
2. A calcareous duricrust.
caldera
A volcanic feature formed by the collapse of land following a volcanic eruption.
Cambrian
The earliest geologic period of the Paleozoic Era, lasting from 541.0 ± 1.0 to 485.4 ± 1.9 million years ago and succeeded by the Ordovician.
carbon film
A type of fossil or preservation.
carbonate
A salt or ester of carbonic acid.
carbonate hardgrounds
Surfaces of synsedimentarily-cemented carbonate layers that have been exposed on the seafloor.
casting
The process which occurs when a liquid fills a cavity and then solidifies. If the cavity originated from the decomposition of dead organisms, casting may result in the formation of fossils.
Cenozoic Era
The most recent of the geological eras, which followed the Mesozoic Era.
chalk
A soft, white, porous sedimentary rock, a form of limestone composed of calcite coccolith plates.
chert
A fine-grained, silica-rich, microcrystalline, cryptocrystalline or microfibrous sedimentary rock that sometimes contains small fossils.
chlorite
Any of a set of allied minerals which may be regarded as hydrated silicates of aluminium, iron, and magnesium. They crystallise in the monoclinic system and are green in colour. They occur as alteration products of such minerals as biotite and hornblende, and also in schistose rocks.
clast
Any individual constituent grain or fragment of a sediment or rock produced by mechanical weathering of a rock mass.
clastic rocks
Mechanically redeposited remains of eroded older rocks; rocks formed of fragments, or clasts, of pre-existing rocks.
clay
cleavage
The tendency of a rock to break along preferred planes of weakness, caused by the development of a planar fabric as a result of deformation.
cobble
coccolith
An individual plate of calcium carbonate formed by coccolithophores which are arranged around them in a so-called coccosphere.
coccolithophore
Also called a coccolithophorid.
A type of microfossil of single-celled algae, protists and phytoplankton belonging to the division of haptophytes. These fossils are distinguished by special calcium carbonate plates called coccoliths.
compaction
The process by which a newly deposited sediment progressively loses its original water content due to the effects of loading. This forms part of the process of lithification.
compression
The process by which rocks shorten or decrease in volume when exposed to certain forces.
conchoidal
A type of fracture that results in smoothly curved surface faces.
concretion
A volume of sedimentary rock in which a mineral cement fills the porosity (i.e. the spaces between the sediment grains).
conglomerate
Any type of rock consisting of individual stones that have become cemented together.
contact metamorphism
Metamorphism due to the local heating of rocks by the intrusion of magma nearby.
continental crust
The layer of granitic, sedimentary, and metamorphic rocks which form the parts of the Earth's crust that comprise the continents, and the areas of shallow seabed close to their shores (known as continental shelves).
continental margin
Zone of the ocean floor, separating the thin oceanic crust from thicker continental crust.
continental shelf
Extended perimeter of a continent and its associated coastal plain, which is covered, during interglacial periods (such as the current epoch), by gulfs, and relatively shallow seas known as shelf seas.
convergent boundary
The boundary between two tectonic plates that are moving toward each other. Contrast divergent boundary.
copal
A type of resin produced by plant or tree secretions, particularly identified with the forms of aromatic tree resins used by the cultures of pre-Columbian Mesoamerica as a ceremonially burned incense, as well as for a number of other purposes.
coprolite
A fossilized specimen of human or animal dung.
cordierite
A silicate of aluminium, iron and magnesium with water, which crystallises in the orthorhombic system and occurs mainly in metamorphic rocks.
core
The innermost layer(s) of a planet, referring especially to the Earth's core.
corestone
An ellipsoidal or broadly rectangular joint block of granite formed by subsurface weathering in the same manner as a tor but entirely separated from bedrock.
country rock
The rock native to an area, as opposed to rock that formed elsewhere and was later transported to the area.
craton
An old and stable part of the continental crust that has survived the merging and splitting of continents and supercontinents for at least 500 million years.
cross-bedding
An inclined sedimentary structure in a horizontal unit of rock. Such tilted structures indicate the type of depositional environment, not post-depositional deformation.
crude oil
A liquid mixture of naturally occurring hydrocarbons.
crust
The outermost solid layer of a planet or moon, referring especially to the Earth's crust.
cryptocrystalline
crystal
crystal habit
crystallinity
D
dacite
An igneous, volcanic rock with a high iron content. It is an extrusive rock of the same general composition as andesite, but a less calcic feldspar. Synonymous with quartz andesite.
daughter product
Any distinct isotope produced by the radioactive decay of an atomic nucleus.
delta
A landform where the mouth of a river flows into an ocean, sea, desert, estuary, lake or another river.
degradation
The lowering of a fluvial surface, such as a stream bed or floodplain, through erosional processes.
dendrite
A crystal that develops with a typical multi-branching tree-like form.
deposition
The geological process by which material is added to a landform or landmass.
detachment fault
A major fault in a mountain belt above which rocks have been intensely folded or faulted.
diagenesis
The process of chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration (weathering) and metamorphism.
diamictite
A comprehensive non-generic term for a non-sorted or poorly sorted non-calcareous terrigenous sedimentary rock that contains a wide range of particle sizes such as rock with sand or larger particles in a muddy matrix.
diapir
A type of intrusion in which a more mobile and ductily deformable material is forced into brittle overlying rocks; a dome or anticlinal fold of the overlaying rocks which has been ruptured by the squeezing out of the plastic core material.
diatomite
A soft, chalk-like sedimentary rock that is easily crumbled into a fine white to off-white powder.
diopside
A monoclinic pyroxene, ideally consisting of silicate of calcium and magnesium, but commonly containing a variable content of FeSi2O6 in addition, and then strictly known as ferriferous diopside.
diorite
A grey to dark grey intermediate intrusive igneous rock composed principally of plagioclase feldspar (typically andesine), biotite, hornblende, and/or pyroxene.
dike
Also spelled dyke.
A type of sheet intrusion referring to any geologic body that cuts discordantly across. A form of minor intrusion injected into the crust during its subjection to tension, the dyke being thin with parallel sides, and maintaining a constant direction in some cases for long distances. Some are more resistant to weathering than the surrounding rock and stand up like walls, while others weather faster and form long narrow depressions.
dip slope
A geological formation often created by erosion of tilted strata.
disconformity
A surface that represents missing rock strata but beds above and below that surface are parallel to one another.
divergent boundary
The boundary separating two tectonic plates that are moving away from each other. Contrast convergent boundary.
dolomite
A sedimentary carbonate rock and mineral, both composed of crystalline calcium magnesium carbonate CaMg(CO3)2.
dolerite
1. A basic igneous rock of medium grain size, occurring as minor intrusions or in the central parts of thick lava flows.
2. A dark-coloured, basic, igneous rock, composed essentially of pyroxene and a triclinic feldspar with magnetic iron. Considered by some authors to be equivalent to a coarse-grained basalt.
3. A dark, crystalline, igneous rock, chiefly pyroxene with labradorite.
4. Coarse-grained basalt.
5. Diabase.
6. Any dark igneous rock composed chiefly of silicates of iron and magnesium with some feldspar.
drill core
A drill specifically designed to remove a cylinder of material, much like a hole saw.
drumlin
An elongated, whale-shaped hill formed by glacial action.
dunite
An ultrabasic plutonic rock in which the mafic material is almost entirely olivine, with accessory chromite almost always present. Feldspar mainly plagioclase. See also peridotite.
duricrust
A general term for hard crust existing as a layer in or on the surface of the upper horizons of a soil in semi-arid climates. Duricrust is formed by the accumulation of solid minerals deposited by water moving upwards by capillary action and evaporating in the dry season. Compare hardpan.
E
earthquake
eclogite
A generally coarse- to medium-grained pyroxene in which are set red garnets. The colour is pistachio green when fresh, but mottled with red when weathered.
Eemian transgression
The portion of the Late Pleistocene spanning the period between 120 Ka and 8m before present.
eon
The largest unit of geologic time.
epicenter
The point on the Earth's surface that is directly above the hypocenter or focus at which an earthquake or underground explosion originates.
epidiorite
Any of a set of altered gabbroic and doleritic rocks in which the original pyroxene has been replaced by fibrous amphibole. The rock may be regarded as a first step in the conversion by dynamothermal metamorphism of a basic igneous rock into a green schist.
epirogenetic
The simultaneous rising and falling movements of continents, maintaining isostasy.
epoch
A division of the standard geologic time scale subordinate to periods. An example is the Pleistocene Epoch of the Quaternary Period.
erosion
The displacement of solids (sediment, soil, rock and other particles) usually by the agents of currents such as wind, water, or ice by downward or down-slope movement in response to gravity or by living organisms (in the case of bioerosion).
erratic
A piece of rock that deviates from the size and type of rock native to the area in which it rests. Erratics usually occur as stones ranging in size from pebbles to large boulders which were transported by glacial ice, which upon melting left them stranded far from their original source. The name "erratic" is based on the errant location of these boulders.
escarpment
A transition zone between different physiogeographic provinces that involves an elevation differential, characterized by a cliff or steep slope.
esker
A long, winding ridge of stratified sand and gravel, examples of which occur in glaciated and formerly glaciated regions of Europe and North America. Eskers are frequently several miles in length and, because of their peculiar uniform shape, somewhat resemble railroad embankments.
estuary
A semi-enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea.
eugeosyncline
A geosyncline in which volcanism is associated with clastic sedimentation; the volcanic part of an orthosyncline located away from the craton.
euhedral
Bounded by the crystal faces peculiar to the species, used of minerals. Synonymous with idiomorphic.
eustatic movements
Changes of sea level, constant over wide areas, due to alterations in the volume of the oceans resulting from the formation or melting of ice caps.
evaporite
Any of a diverse set of water-soluble mineral sediments that result from the evaporation of bodies of surface water.
exfoliation
The stripping of concentric rock slabs from the outer surface of a rock mass.
extension
Strain involving an increase in length. Extension can cause thinning and faulting.
extrusive
A mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff.
F
facies
The sum of the lithological and faunal characters of a sediment is its facies. Lithological facies involves composition, grain size, texture, colour, as well as such mass characteristics as current bedding, nature of stratification, ripple marks, etc. Similarly, metamorphic facies involves the degree of crystallisation and the mineral assemblage in a group of metamorphic rocks.
fanning
Rock deformation related to shear stress.
fault
A discrete planar rock fracture which shows evidence of a displacement (the throw of the fault). A fault is a discrete surface.
fault zone
The zone where exist different discrete fault planes.
feldspar
Any of a set of the most common minerals in the Earth's crust. All feldspars contain silicon, aluminium, and oxygen and may contain potassium, calcium and sodium.
fels
A massive metamorphic rock lacking schistosity or foliation.
felsic
Silicate minerals, magmas, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Light minerals (quartz and feldspar) greater than 60% - acid. [Granite (Rhyolite), Adamellite (Rhyo-dacite), Granodiorite (Dacite)]. The term is a mnemonic adjective for igneous rocks having light-coloured minerals in their mode, from "feldspar" and "silica". Contrast mafic.
ferricrete
A conglomerate consisting of surficial sand and gravel cemented into a hard mass by iron oxide derived from oxidation of percolating solution of iron salts. A ferruginous duricrust.
ferromagnesian mineral
Any iron/magnesium-bearing mineral, such as augite, hornblende, olivine, or biotite.
fission track dating
A method that uses tracks that are visible under the microscope to date minerals.
Flandrian transgression
fold
A stack of originally flat and planar surfaces, such as sedimentary strata, which have become bent or curved as a result of plastic (i.e. permanent) deformation.
foliation
The parallel alignment of textural and structural features of a rock.
fossil
Any mineralized or otherwise preserved remains or traces (such as footprints) of animals, plants, or other once-living organisms.
fossiliferous
Bearing or being composed of fossils in rocks or strata.
fossilization
fracture
Any crack or discontinuity. In its geological definition, it is only used when no displacement can be distinguished.
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G
Ga
A non-standard but widely used abbreviation for one billion (1,000,000,000) years, using the metric prefix G (for "Giga") to indicate a quantity of one billion. When not otherwise qualified, it usually indicates 1,000,000,000 years Before Present (or 1,000,000,000 years ago).
gabbro
A dark, coarse-grained, intrusive igneous rock chemically equivalent to basalt.
garnet
gastrolith
A rock which is or was once held inside the digestive tract of a living animal.
gemology
Also spelled gemmology.
gemstone
Also called a gem, fine gem, jewel, precious stone, or semi-precious stone.
geologic map
A special-purpose map made to show geological features.
geological time scale
Also geologic time scale.
geology
geosyncline
A mobile down-warping of the Earth's crust, either elongate or basin-like, measured in scores of kilometres, which is subsiding as sedimentary and volcanic rocks accumulate to thicknesses of thousands of metres.
glass
A hard, brittle, transparent solid, such as used for windows, many bottles, or eyewear, including soda-lime glass, acrylic glass, sugar glass, isinglass (Muscovy-glass), or aluminium oxynitride.
glauconite
A green-coloured, hydrated silicate mineral of potassium and iron that forms on submerged banks. Its occurrence in sands and sandstones is considered an indication of accumulation under marine conditions.
gneiss
A coarse-grained, pale-coloured gneissose rock, containing abundant feldspar with quartz, mica, hornblende, and garnet.
Gondwanaland
The southern part of the supercontinent of Pangaea which eventually separated to form present-day South America, Africa, India, Australia and Antarctica.
graben
A depressed block of the Earth's crust bordered by parallel faults.
granite
A coarse-grained, often porphyritic, intrusive, felsic, igneous rock containing megascopic quartz, averaging 25%, much feldspar (orthoclase, microcline, sodic plagioclase) and mica or other coloured minerals. Rhyolite is the volcanic equivalent.
granitoid
Any granite-like rock, including granodiorite, diorite, monzonite, and granite itself, among others.
granoblastic
An arrangement of mineral grains in a rock of metamorphic origin similar to that of a normal granite, but produced by recrystallisation in the solid and not by crystallisation from a molten condition.
granodiorite
An intrusive, felsic, igneous rock similar to granite but containing more plagioclase than potassium feldspar. Dacite is the volcanic equivalent.
gravel
graywacke
A variety of sandstone generally characterized by its hardness, dark colour, and poorly sorted, angular grains of quartz, feldspar, and small rock fragments (lithic fragments) set in a compact, clay-fine matrix. Also spelled greywacke.
greenstone
An omnibus term lacking precision and applied indiscriminately to basic and intermediate igneous rocks of Lower Paleozoic age in which much chlorite has been produced at the expense of the original coloured minerals, staining the rocks green.
grus
Freshly eroded, angular grains of quartz and feldspar derived from a granitoid.
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H
habit
See crystal habit.
half-life
The time it takes for a given amount of a radioactive isotope to be reduced by one-half.
hardpan
hemicrystalline
Having the properties of certain rocks of igneous origin which contain some interstitial glass in addition to crystalline minerals. Contrast holocrystalline.
hinge
The zone of maximum curvature of a fold.
hinge line
A line joining the points of maximum curvature along the hinge of a fold.
holocrystalline
Having the properties of those igneous rocks in which all of the components are crystalline; glass is absent. Contrast hemicrystalline.
hornblende
An important rock-forming mineral of complex composition, essentially a silicate of calcium, magnesium and iron, with smaller amounts of potash, soda and hydroxyl. Hornblende crystallises in the monoclinic system and occurs as black crystals or grains in many different types of igneous and metamorphic rocks, including hornblende-granite, syenite, diorite, andesite, hornblende-schist, and amphibole.
hornfels
A hard, compact, fine-textured contact-altered argillaceous rock that breaks into splintery fragments.
horst
A raised fault block bounded by normal faults.
hot spring
A natural spring resulting from the emergence of geothermally heated groundwater from beneath the Earth's crust.
hydrothermal
Pertaining to the actions or products of heated water.
hydrothermal vent
A fissure in a planet's surface from which geothermally heated water emerges.
hypersaline
Having a saltiness or dissolved salt content greater than that of seawater.
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I
ichnology
A branch of biology that deals with traces of organismal behavior.
idiomorphic
Bounded by the crystal faces peculiar to the species, used of minerals. Synonymous with euhedral.
igneous rock
A type of rock formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.
ignimbrite
Fine-grained to aphanitic, buff to dark brown compact rock with parallel streaks or lenticles of black glass, produced by violently explosive volcanoes.
ilmenite
An oxide of iron and titanium, crystallising in the trigonal system; a widespread accessory mineral in igneous rocks, especially those of basic composition.
indurated
Made hard (by heat or compaction).
interbedded
beds (layers) of rock lying between or alternating with beds of a different kind of rock.
intrusion
body of igneous rock that has crystallized from molten magma below the surface of the Earth.
island arc
A chain of volcanic islands or mountains formed by plate tectonics as an oceanic tectonic plate subducts under another tectonic plate and produces magma.
isomorphic
Two crystals that have similar shapes and sizes, usually through the angles.
isotope
different forms of an element each having different atomic mass (mass number).
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J
joint
A discrete discontinuity surface without evidence of displacement. See also diaclase or bedding.
Jurassic
A major unit of the geologic timescale that extended from about 199.6 ± 0.6 Ma (million years ago) to 145.4 ± 4.0 Ma, between the end of the Triassic and the beginning of the Cretaceous.
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K
Ka
A non-standard but widely used abbreviation for one thousand (1,000) years, using the metric prefix K (for "Kilo") to indicate a quantity of one thousand. When not otherwise qualified, it usually indicates 1,000 years Before Present (or 1,000 years ago).
kame
An irregularly shaped hill or mound composed of sand, gravel and till that accumulates in a depression on a retreating glacier and is then deposited on the land surface with further melting of the glacier.
kaolinite
A finely crystalline form of hydrated aluminium silicate occurring as minute monoclinic flaky crystals with a perfect basal cleavage, resulting mainly from the alteration of feldspars under conditions of hydrothermal or pneumatolytic metamorphism.
karst
A distinct type of landscape shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite. Karst topography is usually characterised by closed depressions or sinkholes, caves and underground drainage.
kettle
A fluvioglacial landform occurring as the result of blocks of ice calving from the front of a receding glacier and becoming partially to wholly buried by glacial outwash.
kink
A tight curl, twist, or bend in a rock band. See also folding and buckling.
kink band
An asymmetric, linear zone of deformation characterised by a tight curled, twisted, or bended rock band. Kink bands may also occur as conjugated sets.
kyanite
A silicate of aluminium which crystallises in the triclinic system. It usually occurs as long-bladed crystals, blue in colour, in metamorphic rocks.
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L
lacuna
A time-stratigraphic unit representing the gap in the stratigraphic record. Specifically the missing interval at an unconformity, representing the interpreted space-time value of both hiatus (period of non-deposition), and degradation vacuity (period of erosion).
lamprophyre
Igneous rocks usually occurring as dykes intimately related to larger intrusive bodies; characterised by abnormally high contents of coloured silicates, such as biotite, hornblende and augite, and a correspondingly small amount of feldspar, some being feldspar-free.
lava
Molten rock expelled by a volcano during an eruption.
leucocratic
A term used to denote a light colour in igneous rocks, due to a high content of felsic minerals and a correspondingly small amount of dark, heavy silicates.
limestone
A sedimentary rock composed largely of the mineral calcite (calcium carbonate: CaCO3).
liquefaction
Soil liquefaction describes the behavior of soils that, when loaded, suddenly suffer a transition from a solid state to a liquefied state, or having the consistency of a heavy liquid.
lithic fragment
Also simply called a lithic.
A sand-sized grain that is made up of smaller than sand-sized grains, e.g. a shale fragment or basalt fragment in a sandstone.
lithification
The process by which sediments compact under pressure, expel connate fluids, and gradually become solid rock.
lithology
A description of the physical characteristics of a rock unit visible at outcrop, in hand or core samples or with low magnification microscopy, such as colour, texture, grain size, or composition.
lithotype
Specific types of rock classified according to the standards of lithology.
loess
A fine, silty, pale yellow or buff-coloured, windblown (eolian) type of unconsolidated deposit.
lustre
Also spelled luster.
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M
Ma
A non-standard but widely used abbreviation for one million (1,000,000) years, using the metric prefix M (for "Mega") to indicate a quantity of one million. When not otherwise qualified, it usually indicates 1,000,000 years Before Present (or 1,000,000 years ago).
mafic
A silicate mineral or rock that is rich in magnesium and iron. A mnemonic term for the ferromagnesian and other non-felsic minerals actually present in an igneous rock rich in dark (ferromagnesian) minerals (greater than 60% by volume). Basic [alkali gabbro (alkali basalt), syeno-gabbro (trachybasalt), gabbro (basalt and dolerite)].
magma
Molten rock that sometimes forms beneath the surface of the Earth (or other terrestrial planets) and often collects in a magma chamber.
magnetite
An oxide of iron which crystallises in the cubic system. It is attracted by a magnet but does not attract iron itself.
Malmesbury group
An 830 to 980 Ma basal group of the Western Cape comprising at least eight distinct formations, including the Tygerberg, Piketberg, Porterville, Berg river, Klipplaat, Moorreesburg, Franschhoek, and Bridgetown formations.
mantle
The highly viscous layer of molten rock situated directly beneath the Earth's crust and above the outer core.
marble
A fine to coarse-grained granoblastic calcium carbonate that effervesces in dilute hydrochloric acid. Often banded with various colours and sometimes veined.
marine terrace
A narrow, flat area often seen at the base of a sea cliff caused by the action of the waves.
marl
A calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite.
massive
A description applied to a homogeneous rock which lacks internal structure or layers.
mélange
Large-scale breccia formed in the accretionary wedge above a subduction zone.
melanocratic
A term applied to rocks which are abnormally rich in dark and heavy ferro-magnesium minerals.
mesocratic
A term applied to igneous rocks which in respect of their content of dark silicates are intermediate between those of leucocratic and melanocratic type, and contain 30–60% of dark heavy minerals.
Mesozoic
The era of geological time including the Triassic, Jurassic, and Cretaceous ages.
metamorphic rock
metamorphism
The solid state recrystallisation of pre-existing rocks due to changes in heat and/or pressure and/or the introduction of fluids, i.e. without melting.
metapelite
A metamorphosed pelite rock.
metasilicate
A salt of metasilicic acid H2SiO3.
metatexis
Low-grade anatexis: partial or differential melting of rock components with low melting point.
mica
Any of a set of minerals which crystallise in the monoclinic system. They have similar chemical compositions and highly perfect basal cleavage.
micropaleontology
A branch of paleontology which studies microfossils.
mid-oceanic ridge
An underwater mountain range typically having a valley known as a rift running along its axis, formed by plate tectonics.
migmatite
A composite rock composed of igneous or igneous-looking and/or metamorphic materials which are generally distinguishable megascopically.
mineral
mineralization
The hydrothermal deposition of economically important metals in the formation of ore bodies or "lodes".
mineralogy
miogeosyncline
A geosyncline in which volcanism is not associated with sedimentation, or the non-volcanic part of the orthogeosyncline located near the craton.
Mohs scale of mineral hardness
Also simply called the Mohs scale.
molasse
A partly marine, partly continental or deltaic sedimentary facies consisting of a very thick sequence of soft ungraded cross-bedded fossiliferous conglomerates, sandstones, shales, and marls.
molding
The process of manufacturing by shaping pliable raw material using a rigid frame or model called a mold.
monocline
A fold with a single limb which produces a sudden steepening of the dip; the rocks, however, soon approximate to horizontal on either side of this flexure.
monoclinic
Having three crystal axes of unequal lengths, with one intersection oblique and the other two perpendicular.
moraine
A glacially formed accumulation of unconsolidated debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past ice age.
mullion
A particular type of reworked boudin. The term is likely derived from an architectural structure with the same name.
muscovite
The common or white mica; for the most part an orthosilicate of aluminium and potassium that crystallises in the monoclinic system.
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N
Namibian age
900 to 542 Ma (Neoproterozoic).
Neogene
A geologic period starting 23 million years ago and, depending on definition, either lasting until today or ending 2.6 million years ago with the beginning of the Quaternary.
non-clastic
Having the properties of any chemically and/or organically deposited rock, such as limestones, chalks, and evaporite deposits.
normal fault
Also called an extensional fault.
Dip-slip faults can be sub-classified into the types "reverse" and "normal". A normal fault occurs when the crust is extended such that the hanging wall moves downward relative to the footwall. Contrast reverse fault.
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O
obsidian
oligoclase
One of the plagioclase feldspars consisting of the albite and anorthite molecules combined in the proportions 9:1 to 7:3. It is found especially in the more acid igneous rocks.
olivine
An orthosilicate mineral of iron and magnesium which crystallises in the orthorhombic system and occurs widely in the basic and ultramafic igneous rocks. It includes olivine-gabbro, olivine–dolerite, olivine-basalt, and peridotites, among others.
Ordovician
A geologic period and system, the second of six of the Paleozoic Era, spanning the time between 485.4 ± 1.9 to 443.4 ± 1.5 million years ago. It follows the Cambrian and is followed by the Silurian.
orogenesis
The formation and growth of mountains related to tectonic activity.
orogeny
Any set of forces and events leading to a large structural deformation of the Earth's lithosphere due to the engagement of tectonic plates. It is the primary mechanism by which mountains are built on continents.
orthoclase
A silicate of potassium and aluminium which crystallises in the monoclinic system and occurs as an essential constituent in granitic and syenitic rocks and as an accessory in many other rock types.
orthogeosyncline
A geosyncline between continental and oceanic cratons containing both volcanic and non-volcanic belts.
orthorhombic
Having a crystal structure with three perpendicular axes all of different lengths.
orthosilicate
An obsolete classification based on salt of hypothetical orthosilicic acid. Compare metasilicate.
oxbow lake
A crescent-shaped lake found within a floodplain or fluvial terrace created by the cut-off and abandonment of an active meander within a river or stream channel.
P
pahoehoe
A type of vesicular, basaltic lava often with a ropy surface texture.
Palaeozoic
Also spelled Paleozoic.
The earliest of the three geologic eras of the Phanerozoic Eon, spanning the time from roughly 541 to 252.2 million years ago. It is the longest of the Phanerozoic eras and is subdivided into six geologic periods: the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. The Paleozoic Era follows the Neoproterozoic Era of the Proterozoic Eon, and is followed by the Mesozoic Era.
paleocurrent
An indication of the direction of fluid flow (at the time of deposition) visible in a rock.
paleontology
palagonite
An alteration product from the interaction of water with volcanic glass of chemical composition similar to basalt or from the interaction between water and basalt melt.
paralithic
A weathered layer of bedrock.
pegmatite
Exceptionally coarse-grained igneous rock.
pelite
A descriptive name for a clastic rock with a grain size of less than 1/16 mm (originally sand or silt).
peridotite
An olive green when fresh, medium brown when weathered, saccharoidal intrusive igneous rock composed mainly of olivine, sometimes with pyroxene.
petrology
The branch of geology that studies the origin, composition, distribution, and structure of rocks.
phenoclast
A large, conspicuous fragment in sediment or sedimentary rock composed of various sizes of material.
phenocryst
A relatively large crystal in an igneous rock.
phyllite
Any of a set of argillaceous rocks in a condition of metamorphism between slate and mica-schist.
phyllonite
A rock that macroscopically resembles phyllite but that is formed by mechanical degradation (mylonization) of initially coarser rocks (e.g., graywacke, granite, or gneiss).
piercing point
A feature that is cut by a fault and moved. Reconstruction of that object can show how much the fault has moved.
pitchstone
A black, opaque volcanic glass that may contain irregular, whitish clusters of minerals. Resembles pitch in appearance.
plate tectonics
The set of natural processes and phenomena which result in large-scale movements of portions of the Earth's lithosphere.
Pleistocene
The geologic epoch which lasted from about 2,588,000 to 11,700 years ago, spanning the world's recent period of repeated glaciations. The Pleistocene is the first epoch of the Quaternary Period and the sixth epoch of the Cenozoic Era.
Pliocene
The geologic period that extends from 5.332 million to 2.588[2] million years Before Present. It is the second-youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene and is followed by the Pleistocene.
plutonic
Having crystallised at depth within the Earth's crust, used of a rock. Plutonic rocks are slow-cooling and coarse-grained and have relatively low temperatures of final consolidation.
plumose structure
A ladder or grid pattern that occurs during jointing that resembles plumes, oriented perpendicular to the stress, hence which usually form parallel to the upper and lower surfaces of the constituent rock unit.
pneumatolysis
The destructive after-action of the concentrated volatile constituents of a magma, effected after the consolidation of the main body of the magma.
polymictic
polysynthetic twinning
porphyroblast
A large mineral crystal in a metamorphic rock which has grown within the finer-grained groundmass.
porphyry
1. A rock that is porphyritic, containing large and small crystals.
2. In mining, a specific deposit containing widely disseminated metals, typically copper.
Precambrian
A non-standard geologic time period immediately preceding the Phanerozoic Eon, divided into several eons of the geologic time scale. It spans from the formation of Earth about 4540 Ma (million years ago) to the beginning of the Cambrian Period, about 541.0 ± 1.0 Ma, when macroscopic hard-shelled animals first appeared in abundance.
precipitate
A rock or mineral precipitated into solid form from an aqueous solution.
prograde metamorphism
Mineral changes in rocks under increasing pressure and/or temperature conditions.
protolith
The source rock from which a metamorphic, or in some rare cases a sedimentary, rock was formed. In most cases the appropriate sedimentary term is "provenance" rather than "protolith", since the material has been transported.
psammite
A general term for a sandstone, most often used to describe a metamorphosed rock unit with a dominantly sandstone protolith.
pseudomatrix
A weaker material (mainly lithic fragments) that becomes crushed and matrix-like in a rock.
pumice
A light-coloured, highly vesicular volcanic rock of very low density.
pyroclastic flow
A fast-moving current of hot gas and rock (collectively known as tephra), which normally hugs the ground and travels downhill or spreads laterally under gravity.
pyroclastic
A volcanic fragment, such as a volcanic bomb, breadcrust bomb, or achnelith.
pyroxene
Any of a set of mineral species which, although falling into different systems (orthorhombic, monoclinic, and triclinic), are closely related in form and structure. They are metasilicates of calcium, magnesium, and iron with manganese, and less often with sodium, potassium, zirconium, and fluorine.
pyroxenite
A coarse-grained, holocrystalline igneous rock consisting mainly of pyroxenes. It may contain biotite, hornblende, or olivine as accessories.
Q
quartzite
A compact, hard, very fine-grained white to creamy white rock which breaks into sharp angular fragments. Quartzite is always associated with other metamorphic rocks, while cemented sandstone is always associated with other sedimentary rocks.
Quaternary
The most recent of the three periods of the Cenozoic Era in the standard geologic time scale. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present.
R
regional metamorphism
Over wide areas resulting from deep burial with consequent rise in temperature and static pressure, usually with the help of folding movements that accompany the formation of mountain ranges.
reticulite
A basaltic pumice in which the walls of the vesicles have collapsed, leaving a network of fine, interconnecting glass threads. It is the lightest rock known.
retrograde metamorphism
The reconstitution of a rock via revolatisation under decreasing temperatures (and usually pressures), allowing the mineral assemblages formed in prograde metamorphism to revert to those more stable at less extreme conditions.
reverse fault
Also called a thrust fault.
Dip-slip faults can be sub-classified into the types "reverse" and "normal". A reverse fault occurs when the crust is compressed such that the hanging wall moves upward relative to the footwall. Contrast normal fault.
rhyolite
An aphanitic, buff to greyish flow-banded rock, often containing spherulites or phenocrysts of quartz and feldspar.
rift
roche moutonnée
An elongated post-glacial rock formation with a smoothed surface on the uphill side and a "plucked" surface on the downhill side.
rock
rudaceous
Having the composition and characteristics of clastic rocks, i.e. coarse-grained sedimentary rocks, conglomerates, and breccias, with a particle size of less than 2 mm.
rudite
Any of a set of sedimentary rocks composed of rounded or angular detrital grains, i.e. granules, pebbles, cobbles, and boulders, which are coarser than sand in size.
S
saccharoidal
Having a texture similar to that of granulated sugar.
Saldanian orogeny
sand
sandstone
Sand (with grains up to 2 mm in diameter) in which the grains are cemented together by secondary silica or calcite. Maybe loosely cemented and soft or well cemented and hard. Buff to brownish; sometimes reddish, due to presence of iron oxides, or greenish, due to presence of glauconite.
sanidine
A form of potash feldspar identical in composition with orthoclase but physically different, formed under different conditions and occurring in different rock types. It is the high temperature form of orthoclase, into which it inverts at 900 °C (1,650 °F). Occurs in lavas and dyke rocks.
schist
A group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. In French, schist is understood as shale.
scree
See talus.
sediment trap
A depression in which sediments substantially accumulate over time.
sedimentary rock
sequence
A sequence of geological events, processes, or rocks arranged in chronological order.
sericite
A white potash-mica, similar to muscovite in chemical composition and general character but occurring as a secondary mineral, often as a decomposition product of orthoclase.
shale
A fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite.
shear zone
A tabular to sheet-like, planar or curviplanar zone composed of rocks that are more highly strained than rocks adjacent to the zone. See also fault.
shield
A large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas.
Shingle beach
A beach which is armoured with pebbles or small- to medium-sized cobbles (as opposed to fine sand), typically ranging from 2 to 200 millimetres (0.1 to 7.9 in) diameter.
silcrete
An indurated soil duricrust formed when surface sand and gravel are cemented by dissolved silica.
silt
Granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment (also known as suspended load) in a surface water body. It may also exist as soil deposited at the bottom of a water body.
slate
Very fine-grained sedimentary rock of the clay or silt grade which as a consequence of regional metamorphism has developed a slaty cleavage.
slaty cleavage
The property of splitting easily along regular, closely spaced planes of fissility, produced by pressure in fine-grained rocks, with the cleavage planes lying in the directions of maximum elongation of the mass.
slickenside
A smoothly polished surface caused by frictional movement between rocks along the two sides of a fault. This surface is normally striated in the direction of movement.
slump
A form of mass wasting that occurs when a coherent mass of loosely consolidated materials or rock layers moves a short distance down a slope.
soil liquefaction
The process describing the behavior of soils that, when loaded, suddenly suffer a transition from a solid state to a liquefied state, or which have the consistency of a heavy liquid.
sorting
Sorting describes the distribution of grain size of sediments, either in unconsolidated deposits or in sedimentary rocks. Very poorly sorted indicates that the sediment sizes are mixed (large variance); whereas well sorted indicates that the sediment sizes are similar (low variance).
sphene
Also called titanite.
A calcium titanium nesosilicate mineral.
staurolite
A red brown to black, mostly opaque, nesosilicate mineral with a white streak.
stone
storm ridge
A beach ridge usually located further or higher inland caused by wave action from storms.
strain
A change in the volume or shape of a rock mass in response to stress.
stratigraphy
stylolite
An irregular discontinuity or non-structural fracture in limestone and other sedimentary rocks. Stylolites result from compaction and pressure solution during diagenesis.
surficial
Of or pertaining to the surface.
syenite
A coarse-grained igneous rock of intermediate composition, composed essentially of alkali-feldspar to the extent of at least two thirds of the total, with a variable content of mafic materials, of which common hornblende is characteristic.
syncline
A geological fold with strata dipping inwards towards the fold axis. Contrast anticline.
syntaxis
T
Table Mountain Group
A group of rock formations within the Cape Supergroup sequence of rocks.
talus
Also called scree.
A collection of broken rock fragments at the base of crags, mountain cliffs, volcanoes or valley shoulders that has accumulated through periodic rockfall from adjacent cliff faces. Landforms associated with these materials are often called talus deposits.
tectonic plate
tektite
Natural glass formed from terrestrial ejecta during a meteorite impact.
tenacity
A mineral's behavior when deformed or broken.
tephra
Fragmental material produced by a volcanic eruption regardless of composition, fragment size or emplacement mechanism. Once clasts have fallen to the ground they remain as tephra unless hot enough to fuse together into pyroclastic rock or tuff.
Tethys Ocean
A prehistoric ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean.
till
Also called glacial till.
Unsorted glacial sediment. Glacial drift is a general term for the coarsely graded and extremely heterogeneous sediments of glacial origin. Glacial till is that part of glacial drift which was deposited directly by the glacier.
tillite
A type of sedimentary rock derived from glacial till which has been indurated or lithified by subsequent burial into solid rock.
topography
The arrangement of the natural and artificial physical features of an area.
tor
A large, free-standing residual mass (rock outcrop) that rises abruptly from the surrounding smooth and gentle slopes of a rounded hill summit or ridge crest.
trace fossil
trachyte
A fine-grained igneous rock type of intermediate composition, in most cases with little or no quartz, consisting largely of alkali-feldspars (sanidene or oligooclase) together with a small amount of coloured silicates such as diopside, horneblende, or mica.
travertine
A terrestrial sedimentary rock formed by the precipitation of carbonate minerals from solution in ground and surface waters and/or geothermally heated hot springs.
triclinic
In the triclinic system, the crystal is described by vectors of unequal length, and none of the three vectors are orthogonal to another.
tuff
A rock formed of compacted volcanic fragments, some of which can be distinguished by the naked eye. If the fragments are larger than the rock grades into an agglomerate.
tundra
A vast, flat, treeless Arctic region of Europe, Asia, and North America in which the subsoil is permanently frozen.
turbidite
The deposit of a turbidity current.
turbidity current
A current of rapidly moving, sediment-laden water moving down a slope through water, or another fluid. The current moves because it has a higher density than the fluid through which it flows.
Tygerberg formation
A component of the PreCambrian Malmesbury group of South Africa
U
ultramafic
Sometimes used interchangeably with ultrabasic.
Almost feldspar-free. Examples of ultramafic rocks include dunite, peridotite, and pyroxenite.
urgonian
A shallow-water carbonate facies deposited along the northern margins of the Tethys Ocean during the Barremian and Aptian.
V
vacuole
A bubble inclusion within mineral grains (typically monocrystalline quartz), filled with liquid, gas, or both liquid and gas. Vacuoles are randomly distributed in contrast to the oriented bubble trains of Boehm Lamellae.
Variscan orogeny
Also called the Hercynian orogeny.
A geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea.
varve
An annual layer of sediment or sedimentary rock.
vein
A mineral filling of a fracture or other crack within a rock in a sheet-like or tabular shape.
vermiculite
A hydrous silicate mineral that is classified as a phyllosilicate and that expands greatly when heated. Exfoliation occurs when the mineral is heated sufficiently.
vergence
The direction of overturning of asymmetric folds, which matches the direction of thrusting.
vesiculated
vitrinite
A group of macerals that are the most common component of coal.
vitrophyre
See pitchstone.
volcanic
Rocks that have crystallised from magma poured out at the surface or introduced at shallow depth. They have cooled relatively rapidly, the grain size of the crystals is small, some part of the melt may solidify as glass, volatiles are lost and anhydrous minerals with high temperatures of crystallisation are present.
volcanic bomb
Rounded or spindle-shaped rock of mainly basaltic composition ejected during eruptions.
vug
A small cavity in a rock filled or lined with crystals or minerals that are different from the host rock.
W
wiggle trace
A graph that plots wave amplitudes (recorded by seismic reflection and borehole logging) as a function of time, with the positive peaks shaded in a single dark colour.
wolframite
An iron manganese tungstate mineral with the chemical formula (Fe,Mn)WO4.
X
xenolith
A rock fragment which becomes enveloped in a larger rock during the latter's development and hardening. In geology, the term is almost exclusively used to describe inclusions in igneous rock during magma emplacement and eruption.
xenotime
A rare earth phosphate mineral whose major component is yttrium orthophosphate (YPO4).
X-ray diffraction (XRD)
A method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and diffracts into many specific directions.
X-ray fluorescence (XRF)
The emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays. The phenomenon is widely used for elemental analysis and chemical analysis of minerals.
xyloid coal
Also called lignite or brown coal.
A soft brown fuel with characteristics that put it somewhere between coal and peat.
Y
yellow cake
Also yellowcake or urania.
A kind of uranium concentrate powder obtained from leach solutions in an intermediate step in the enrichment of uranium ores.
Young's modulus
Also called the tensile modulus.
In solid mechanics, a measure of the stiffness of an isotropic elastic material. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds.
Ypresian
The oldest age or the lowest stratigraphic stage of the Eocene. It spans the time between ~56 Ma and ~49 Ma (million years ago).
Z
zeolite
Microporous, aluminosilicate minerals commonly used as adsorbents.
zircon
A zirconium silicate mineral belonging to the group of nesosilicates. Its corresponding chemical formula is ZrSiO4.
A
Accelerated Graphics Port (AGP)
A high-speed point-to-point channel for attaching a video card to a computer's motherboard, primarily to assist in the acceleration of 3D computer graphics.
accelerator
A microprocessor, ASIC, or expansion card designed to offload a specific task from the CPU, often containing fixed function hardware. A common example is a graphics processing unit.
accumulator
A register in a CPU in which intermediate arithmetic and logic results are stored.
address
The unique integer number that specifies a memory location in an address space.
address space
A mapping of logical addresses into physical memory or other memory-mapped devices.
Advanced Technology eXtended (ATX)
A motherboard form factor specification developed by Intel in 1995 to improve on previous DE factor standards like the AT form factor.
AI accelerator
An accelerator aimed at running artificial neural networks or other machine learning and machine vision algorithms (either training or deployment), e.g. Movidius Myriad 2, TrueNorth, tensor processing unit, etc.
Advanced Configuration and Power Interface
An open standard for operating systems to discover, configure, manage, and monitor status of the hardware.
B
Blu-ray Disc (BD)
An optical disc storage medium designed to supersede the DVD format.
bus
A subsystem that transfers data between computer components inside a computer or between computers.
C
cache
A small, fast local memory that transparently buffers access to a larger but slower or more distant/higher latency memory or storage device, organised into cache lines. Automatically translates accesses to the underlying resources address space to locations in the cache.
cache coherency
The process of keeping data in multiple caches synchronised in a multiprocessor shared memory system, also required when DMA modifies the underlying memory.
cache eviction
Freeing up data from within a cache to make room for new cache entries to be allocated; controlled by a cache replacement policy. Caused by a cache miss whilst a cache is already full.
cache hit
Finding data in a local cache, preventing the need to search for that resource in a more distant location (or to repeat a calculation).
cache line
A small block of memory within a cache; the granularity of allocation, refills, eviction; typically 32–128 bytes in size.
cache miss
Not finding data in a local cache, requiring use of the cache policy to allocate and fill this data, and possibly performing evicting other data to make room.
cache thrashing
A pathological situation where access in a cache cause cyclical cache misses by evicting data that is needed in the near future.
cache ways
The number of potential cache lines in an associative cache that specific physical addresses can be mapped to; higher values reduce potential collisions in allocation.
cache-only memory architecture (COMA)
A multiprocessor memory architecture where an address space is dynamically shifted between processor nodes based on demand.
card reader
Any data input device that reads data from a card-shaped storage medium.[1][2][3]
channel I/O
A generic term that refers to a high-performance input/output (I/O) architecture that is implemented in various forms on a number of computer architectures, especially on mainframe computers.
chipset
Also chip set.
A group of integrated circuits, or chips, that are designed to work together. They are usually marketed as a single product.
Compact Disc-Recordable (CD-R)
A variation of the optical compact disc which can be written to once.
Compact Disc-ReWritable (CD-RW)
A variation of the optical compact disc which can be written to many times.
Compact Disc Read-Only Memory (CD-ROM)
A pre-pressed compact disc which contains data or music playback and which cannot be written to.
computer case
Also chassis, cabinet, box, tower, enclosure, housing, system unit, or simply case.
The enclosure that contains most of the components of a computer, usually excluding the display, keyboard, mouse, and various other peripherals.
An 80×80×25 mm computer fan
computer fan
An active cooling system forcing airflow inside or around a computer case using a fan to cause air cooling.
computer form factor
The name used to denote the dimensions, power supply type, location of mounting holes, number of ports on the back panel, etc.
computer monitor
An electronic visual display for computers. A monitor usually comprises the display device, circuitry, casing, and power supply. The display device in modern monitors is typically a thin film transistor liquid crystal display (TFT-LCD) or a flat panel LED display, whereas older monitors used a cathode ray tube (CRT).[1]
control store
The memory that stores the microcode of a CPU.
Conventional Peripheral Component Interconnect (Conventional PCI)
Also simply PCI.
A computer bus for attaching hardware devices in a computer.
core
The portion of the CPU which actually performs arithmetic and logical operations; many CPUs have multiple cores (e.g. "a quad-core processor").
core memory
In modern usage, a synonym for main memory, dating back from the pre-semiconductor-chip times when the dominant main memory technology was magnetic core memory.
Central Processing Unit (CPU)
The portion of a computer system that executes the instructions of a computer program.
D
data cache (D-cache)
A cache in a CPU or GPU servicing data load and store requests, mirroring main memory (or VRAM for a GPU).
data storage
A technology consisting of computer components and recording media used to retain digital data. It is a core function and fundamental component of computers.[1]
device memory
local memory associated with a hardware device such as a graphics processing unit or OpenCL compute device, distinct from main memory.
Digital Video Disc (DVD)
Also Digital Versatile Disc.
An optical compact disc - of the same dimensions as compact discs (CDs), but store more than six times as much data.
Digital Visual Interface (DVI)
A video display interface developed by the Digital Display Working Group (DDWG). The digital interface is used to connect a video source to a display device, such as a computer monitor.
Direct Access Storage Device (DASD)
A mainframe terminology introduced by IBM denoting secondary storage with random access, typically (arrays of) hard disk drives.
direct mapped cache
A cache where each physical address may only be mapped to one cache line, indexed using the low bits of the address. Simple but highly prone to allocation conflicts.
direct memory access (DMA)
The ability of a hardware device such as a disk drive or network interface to access main memory without intervention from the CPU, provided by one or more DMA channels in a system.
DisplayPort
A digital display interface developed by the Video Electronics Standards Association (VESA). The interface is primarily used to connect a video source to a display device such as a computer monitor, though it can also be used to transmit audio, USB, and other forms of data.
drive bay
A standard-sized area within a computer case for adding hardware (hard drives, CD drives, etc.) to a computer.
dual in-line memory module (DIMM)
A series of dynamic random-access memory integrated circuits. These modules are mounted on a printed circuit board and designed for use in personal computers, workstations and servers. Contrast SIMM.
dual issue
A superscalar pipeline capable of executing two instructions simultaneously.
dynamic random-access memory (DRAM)
A type of random-access memory that stores each bit of data in a separate capacitor within an integrated circuit and which must be periodically refreshed to retain the stored data.
E
expansion bus
A computer bus which moves information between the internal hardware of a computer system (including the CPU and RAM) and peripheral devices. It is a collection of wires and protocols that allows for the expansion of a computer.
A PCI digital I/O expansion card
expansion card
A printed circuit board that can be inserted into an electrical connector or expansion slot on a computer motherboard, backplane, or riser card to add functionality to a computer system via an expansion bus.
F
firewall
Any hardware device or software program designed to protect a computer from viruses, trojans, malware, etc.
firmware
Fixed programs and data that internally control various electronic devices.
flash memory
A type of non-volatile computer storage chip that can be electrically erased and reprogrammed.
floppy disk
A data storage medium that is composed of a disk of thin, flexible ("floppy") magnetic storage medium encased in a square or rectangular plastic shell.
floppy disk drive
A device for reading floppy disks.
floppy-disk controller
free and open-source graphics device driver
G
graphics hardware
Graphics Processing Unit (GPU)
H
hard disk drive (HDD)
Any non-volatile storage device that stores data on rapidly rotating rigid (i.e. hard) platters with magnetic surfaces.
hardware
The physical components of a computer system.
Harvard architecture
A memory architecture where program machine code and data are held in separate memories, more commonly seen in microcontrollers and digital signal processors.
High-Definition Multimedia Interface (HDMI)
A compact interface for transferring encrypted uncompressed digital audio and video data to a device such as a computer monitor, video projector or digital television.
I
input device
Any peripheral equipment used to provide data and control signals to an information processing system.
input/output (I/O)
The communication between an information processing system (such as a computer), and the outside world.
Input/Output Operations Per Second (IOPS)
A common performance measurement used to benchmark computer storage devices like hard disk drives.
instruction
A group of several bits in a computer program that contains an operation code and usually one or more memory addresses.
instruction cache
I-cache
A cache in a CPU or GPU servicing instruction fetch requests for program code (or shaders for a GPU), possibly implementing modified Harvard architecture if program machine code is stored in the same address space and physical memory as data.
instruction fetch
A stage in a pipeline that loads the next instruction referred to by the program counter.
integrated circuit
Also chip.
A miniaturised electronic circuit that has been manufactured in the surface of a thin substrate of semiconductor material.
J
jump drive
Another name for a USB flash drive.
K
keyboard
An input device, partially modeled after the typewriter keyboard, which uses an arrangement of buttons or keys to act as mechanical levers or electronic switches.
L
load/store instructions
instructions used to transfer data between memory and processor registers.
load-store architecture
An instruction set architecture where arithmetic/logic instructions may only be performed between processor registers, relying on separate load/store instructions for all data transfers.
local memory
memory associated closely with a processing element, e.g. a cache, scratchpad, the memory connected to one processor node in a NUMA or COMA system, or device memory (such as VRAM) in an accelerator.
M
magneto-optical drive
mainframe
An especially powerful computer used mainly by large organizations for bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.
main memory
The largest random-access memory in a memory hierarchy (before offline storage) in a computer system; i.e. distinct from caches or scratchpads; usually consists of DRAM.
mask ROM
A type of read-only memory (ROM) whose contents are programmed by the integrated circuit manufacturer.
memory
Devices that are used to store data or programs on a temporary or permanent basis for use in an electronic digital computer.
memory access pattern
The pattern with which software or some other system (such as an accelerator or DMA channel) accesses memory, affecting locality of reference and parallelism.
memory address
The address of a location in a memory or other address space.
memory architecture
A memory architecture in a computer system, e.g. NUMA, uniform memory access, COMA, etc.
memory card
mini-VGA
Small connectors used on some laptops and other systems in place of the standard VGA connector.
microcode
A layer of hardware-level instructions involved in the implementation of higher level machine code instructions in many computers and other processors.
modem
modified Harvard architecture
A variation of Harvard architecture used for most CPUs with separate non-coherent instruction and data caches (assuming that code is immutable), but still mirroring the same main memory address space, and possibly sharing higher levels of the same cache hierarchy.
monitor
An electronic visual display for computers.
The Octek Jaguar V motherboard from 1993[4]
motherboard
The central printed circuit board (PCB) in many modern computers which holds many of the crucial components of the system, usually while also providing connection space for peripherals.[5]
mouse
A pointing device that functions by detecting two-dimensional motion relative to its supporting surface; motion is usually mapped to a cursor in screen space; typically used to control a graphical user interface on a desktop computer or for CAD, etc.
N
network
A collection of computers and other devices connected by communications channels, e.g. by Ethernet or wireless networking.
network interface controller
Also LAN card or network card.
[6]
network on a chip (NOC)
A computer network on a single semiconductor chip, connecting processing elements, fixed function units, or even memories and caches. Increasingly common in system on a chip designs.
non-uniform memory access (NUMA)
non-volatile memory
memory that can retain the stored data even when not powered, as opposed to volatile memory.
non-volatile random-access memory
Random-access memory (RAM) that retains its data when power is turned off.
O
operating system
The set of software that manages computer hardware resources and provides common services for computer programs, typically loaded by the BIOS on booting.
operation code
Several bits in a computer program instruction that specify which operation to perform.
optical disc drive
A type of disk drive that uses laser light or electromagnetic waves near the light spectrum as part of the process of reading or writing data to or from optical discs.
P
pen drive
Another name for a USB flash drive.
pentest
Another name for a penetration test.
peripheral
Any device attached to a computer but not part of it.
personal computer (PC)
Any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator.
power supply
A unit of the computer that converts mains AC to low-voltage regulated DC for the power of all the computer components.
power supply unit (PSU)
Converts mains AC to low-voltage regulated DC power for the internal components of a computer. Modern personal computers universally use switched-mode power supplies. Some power supplies have a manual switch for selecting input voltage, while others automatically adapt to the mains voltage.
prefetch
The process of pre-loading instructions or data into a cache ahead of time, either under manual control via prefetch instructions or automatically by a prefetch unit which may use runtime heuristics to predict the future memory access pattern.
prefetching
The pre-loading of instructions or data before either is needed by dedicated cache control instructions or predictive hardware, to mitigate latency.
printer
A peripheral which produces a text or graphics of documents stored in electronic form, usually on physical print media such as paper or transparencies.
process node
Refers to a level of semiconductor manufacturing technology, one of several successive transistor shrinks.
processing element
An electronic circuit (either a microprocessor or an internal component of one) that may function autonomously or under external control, performing arithmetic and logic operations on data, possibly containing local memory, and possibly connected to other processing elements via a network, network on a chip, or cache hierarchy.
processor node
A processor in a multiprocessor system or cluster, connected by dedicated communication channels or a network.
programmable read-only memory (PROM)
A type of non-volatile memory chip that may be programmed after the device is constructed.
programmer
Any electronic equipment that arranges written software to configure programmable non-volatile integrated circuits (called programmable devices) such as EPROMs, EEPROMs, Flashes, eMMC, MRAM, FRAM, NV RAM, PALs, FPGAs or programmable logic circuits.
PCI Express (PCIe)
An expansion bus standard designed to replace the older PCI, PCI-X, and AGP bus standards.
PCI-eXtended (PCI-X)
An expansion bus and expansion card standard that enhances the 32-bit PCI Local Bus for higher bandwidth demanded by servers.
R
Redundant Array of Independent Disks (RAID)
Any of various data storage schemes that can divide and replicate data across multiple hard disk drives in order to increase reliability, allow faster access, or both.
random-access memory (RAM)
A type of computer data storage that allows data items to be accessed (read or written) in almost the same amount of time irrespective of the physical location of data inside the memory. RAM contains multiplexing and demultiplexing circuitry to connect the data lines to the addressed storage for reading or writing the entry. Usually more than one bit of storage is accessed by the same address, and RAM devices often have multiple data lines and are said to be '8-bit' or '16-bit' etc. devices. In today's technology, random-access memory takes the form of integrated circuits.
read-only memory (ROM)
A type of memory chip that retains its data when its power supply is switched off.
S
server
A computer which may be used to provide services to clients.
software
Any computer program or other kind of information that can be read and/or written by a computer.
single in-line memory module (SIMM)
A type of memory module containing random-access memory used in computers from the early 1980s to the late 1990s. Contrast DIMM.
A 2.5-inch solid-state drive that can be used in laptops and desktop computers
solid-state drive
Also solid-state disk or electronic disk.
Any data storage device that uses integrated circuit assemblies as memory to store data persistently. Though they are sometimes referred to as solid-state disks, these devices contain neither an actual disk nor a drive motor to spin a disk.
static random-access memory (SRAM)
A type of semiconductor memory that uses bistable latching circuitry to store each bit. The term static differentiates it from DRAM, which must be periodically refreshed.
sound card
Also audio card.
An internal expansion card that facilitates economical input and output of audio signals to and from a computer under control of computer programs.
storage device
synchronous dynamic random-access memory (SDRAM)
A type of dynamic random access memory that is synchronized with the system bus.
SuperDisk
A high-speed, high-capacity alternative to the 90 mm (3.5 in), 1.44 MB floppy disk. The SuperDisk hardware was created by 3M's storage products group Imation in 1997.
Sata
Also Serial ATA (SATA, abbreviated from Serial AT Attachment)
A computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives.
Contents:
T
tape drive
A peripheral storage device that allows only sequential access, typically using magnetic tape.
terminal
An electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system.
trackpad
Also touchpad.
A pointing device consisting of specialized surface that can translate the motion and position of a user's fingers or a stylus to a relative position on a screen.[7]
TV tuner card
U
Universal Serial Bus (USB)
A specification to establish communication between devices and a host controller (usually a personal computer).
uop cache
A cache of decoded micro-operations in a CISC processor (e.g x86). [8]
USB flash drive
A flash memory device integrated with a USB interface. USB flash drives are typically removable and rewritable.
V
video card
Also graphics card.
An expansion card which generates a feed of output images to a display (such as a computer monitor).
Video Graphics Array (VGA)
The last graphical standard introduced by IBM to which the majority of PC clone manufacturers conformed.
volatile memory
Memory that requires power to maintain the stored information, as opposed to non-volatile memory.
W
A webcam typically includes a lens (shown at top), an image sensor (shown at bottom), and supporting circuitry
webcam
A video camera that feeds its images in real time to a computer or computer network, often via USB, Ethernet, or Wi-Fi.[1][9]
write back cache
A cache where store operations are buffered in cache lines, only reaching main memory when the entire cache line is evicted.
write through cache
A cache where store operations are immediately written to the underlying main memory.
working set
The set of data used by a processor during a certain time interval, which should ideally fit into a CPU cache for optimum performance.
Z
zip drive
The Zip drive is a removable floppy disk storage system that was introduced by Iomega in late 1994. Considered medium-to-high-capacity at the time of its release, Zip disks were originally launched with capacities of 100 MB.
A
AAS – Aarskog-Scott syndrome.
Aarskog–Scott syndrome – A rare, inherited (X-linked) disease characterized by short stature, facial abnormalities, skeletal and genital anomalies.[1]
Abdomen – The part of the body between the chest and pelvis, which contains most of the tubelike organs of the digestive tract, as well as several solid organs.
Abdominal external oblique muscle – The largest, and outermost, of the three flat muscles of the lateral anterior abdominal wall.
Abdominal internal oblique muscle – A muscle of the abdominal wall, which lies below the external oblique and just above the transverse abdominal muscles.
Abductor pollicis brevis muscle – A muscle in the hand that abducts (straightens) the thumb.
Abductor pollicis longus muscle – One of the extrinsic muscles of the hand. Its major function is to abduct the thumb at the wrist.
Abscess – A collection of pus that has built up within the tissue of the body.[2]
Accommodation – the process by which the eye focuses on an object.
Accommodation reflex – a reflex action of the eye, measured as a response to focusing on a near object, then looking at a distant object (and vice versa).
Acetabulum – a concave surface of the pelvis, which forms the pelvic section of the hip joint.[3][4]
Achilles tendon – a tendon of the back of the leg, and the thickest in the human body. It attaches the plantaris, gastrocnemius (calf) and soleus muscles to the calcaneus (heel) bone.
Acne – a long-term skin disease that occurs when hair follicles are clogged with dead skin cells and oil from the skin.[5]
Acne vulgaris – see Acne
Acupressure – an alternative medicine technique where pressure is applied to acupuncture points. Pressure may be applied by hand, by elbow, or with various devices.
Acupuncture – a form of alternative medicine[6] in which thin needles are inserted into the body.[7]
Adam's apple – the lump or protrusion that is formed by the angle of the thyroid cartilage surrounding the larynx seen especially in males.
Adaptive immune system – also known as the acquired immune system or, more rarely, as the specific immune system, is a subsystem of the overall immune system that is composed of highly specialized, systemic cells and processes that eliminate pathogens or prevent their growth.
Adenoma – (plural adenomas or adenomata) is a benign tumor of epithelial tissue with glandular origin, glandular characteristics, or both.
Adrenal gland – The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol.[8][9] They are found above the kidneys.
Allergy – Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment.[10] These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis.[11] Symptoms may include red eyes, an itchy rash, sneezing, a runny nose, shortness of breath, or swelling.[12] Food intolerances and food poisoning are separate conditions.[13][14]
ADHD – Attention deficit hyperactivity disorder.
Alzheimer's disease – (AD), also referred to simply as Alzheimer's, is a chronic neurodegenerative disease that usually starts slowly and worsens over time.[15][16] It is the cause of 60–70% of cases of dementia.[15][16] The most common early symptom is difficulty in remembering recent events (short-term memory loss).[15]
Anal canal – is the terminal part of the large intestine.[17] It is situated between the rectum and anus,[18] below the level of the pelvic diaphragm. In humans it is approximately 2.5 to 4 cm (0.98-1.58 in) long. It lies in the anal triangle of perineum in between the right and left ischioanal fossa.
Anatomy – is the branch of biology concerned with the study of the structure of organisms and their parts.[19] Anatomy is a branch of natural science which deals with the structural organization of living things.
Anesthesiology – Anesthesiology, anaesthesiology, anaesthesia or anaesthetics (see Terminology) is the medical speciality concerned with the total perioperative care of patients before, during and after surgery.[20]
Angiology – is the medical specialty which studies the diseases of the circulatory system and of the lymphatic system, i.e., arteries, veins and lymphatic vessels, and its diseases.
Ankle – The ankle, or the talocrural region,[21] is the region where the foot and the leg meet.[22] The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular joint.[23][24][25] The movements produced at this joint are dorsiflexion and plantarflexion of the foot. In common usage, the term ankle refers exclusively to the ankle region. In medical terminology, "ankle" (without qualifiers) can refer broadly to the region or specifically to the talocrural joint.[21][26]
Anterior tibial artery – The anterior tibial artery of the leg carries blood to the anterior compartment of the leg and dorsal surface of the foot, from the popliteal artery.
Antibiotic – is a type of antimicrobial substance active against bacteria and is the most important type of antibacterial agent for fighting bacterial infections. Antibiotic medications are widely used in the treatment and prevention of such infections.[27][28]
Antibody – (Ab), also known as an immunoglobulin (Ig),[29] is a large, Y-shaped protein produced mainly by plasma cells that is used by the immune system to neutralize pathogens such as pathogenic bacteria and viruses.
Aorta – is the main artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries (the common iliac arteries). The aorta distributes oxygenated blood to all parts of the body through the systemic circulation.[30]
Appendix – The appendix (or vermiform appendix; also cecal [or caecal] appendix; vermix; or vermiform process) is a finger-like, blind-ended tube connected to the cecum, from which it develops in the embryo. The cecum is a pouch-like structure of the colon, located at the junction of the small and the large intestines. The term "vermiform" comes from Latin and means "worm-shaped." The appendix used to be considered a vestigial organ, but this view has changed over the past decades.[31]
Arm – is the part of the upper limb between the glenohumeral joint (shoulder joint) and the elbow joint. In common usage, the arm extends to the hand. It can be divided into the upper arm, which extends from the shoulder to the elbow, the forearm which extends from the elbow to the hand, and the hand. Anatomically the shoulder girdle with bones and corresponding muscles is by definition a part of the arm. The Latin term brachium may refer to either the arm as a whole or to the upper arm on its own.[32][33][34]
Arteriole – is a small-diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries.[35] Arterioles have muscular walls (usually only one to two layers of smooth muscle) and are the primary site of vascular resistance. The greatest change in blood pressure and velocity of blood flow occurs at the transition of arterioles to capillaries.
Artery – is a blood vessel that takes blood away from the heart to all parts of the body (tissues, lungs, etc). Most arteries carry oxygenated blood; the two exceptions are the pulmonary and the umbilical arteries, which carry deoxygenated blood to the organs that oxygenate it. The effective arterial blood volume is that extracellular fluid which fills the arterial system.
Arthritis – is a term often used to mean any disorder that affects joints.[36] Symptoms generally include joint pain and stiffness.[36] Other symptoms may include redness, warmth, swelling, and decreased range of motion of the affected joints.[36][37]
AS – Asperger syndrome.
Asperger syndrome – (AS), also known as Asperger's, is a developmental disorder characterized by significant difficulties in social interaction and nonverbal communication, along with restricted and repetitive patterns of behavior and interests.[38] As a milder autism spectrum disorder (ASD), it differs from other ASDs by relatively normal language and intelligence.[39] Although not required for diagnosis, physical clumsiness and unusual use of language are common.[40][41]
Asthma – is a common long-term inflammatory disease of the airways of the lungs.[42] It is characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm.[43] Symptoms include episodes of wheezing, coughing, chest tightness, and shortness of breath.[44]
Atrial fibrillation – (AF or A-fib) is an abnormal heart rhythm characterized by rapid and irregular beating of the atria.[45] Often it starts as brief periods of abnormal beating which become longer and possibly constant over time.[46] Often episodes have no symptoms.[47]
Attention deficit hyperactivity disorder – is a mental disorder of the neurodevelopmental type.[48][49] It is characterized by problems paying attention, excessive activity, or difficulty controlling behavior which is not appropriate for a person's age.[50][51]
Auscultation – is listening to the internal sounds of the body, usually using a stethoscope. Auscultation is performed for the purposes of examining the circulatory and respiratory systems (heart and breath sounds), as well as the gastrointestinal system.
Autism – is a developmental disorder characterized by troubles with social interaction and communication, and by restricted and repetitive behavior.[51] Parents usually notice signs during the first two or three years of their child's life.[52][51] These signs often develop gradually, though some children with autism reach their developmental milestones at a normal pace before worsening.[53]
Axilla – (also, armpit, underarm or oxter) is the area on the human body directly under the joint where the arm connects to the shoulder. It also provides the under-arm sweat gland.
Axillary artery – is a large blood vessel that conveys oxygenated blood to the lateral aspect of the thorax, the axilla (armpit) and the upper limb. Its origin is at the lateral margin of the first rib, before which it is called the subclavian artery.
B
Back – The human back is the large posterior area of the human body, rising from the top of the buttocks to the back of the neck and the shoulders. It is the surface of the body opposite from the chest. The vertebral column runs the length of the back and creates a central area of recession. The breadth of the back is created by the shoulders at the top and the pelvis at the bottom.
Back pain – is pain felt in the back. It is divided into neck pain (cervical), middle back pain (thoracic), lower back pain (lumbar) or coccydynia (tailbone or sacral pain) based on the segment affected.[54] The lumbar area is the most common area for pain, as it supports most of the weight in the upper body.[55] Episodes of back pain may be acute, sub-acute, or chronic depending on the duration. The pain may be characterized as a dull ache, shooting or piercing pain, or a burning sensation. Discomfort can radiate into the arms and hands as well as the legs or feet, and may include numbness,[54] or weakness in the legs and arms.
Beta cell – Beta cells (β cells) are a type of cell found in pancreatic islets that synthesize and secrete insulin. Beta cells make up 50-70% of the cells in human islets.[56] In patients with type I or type II diabetes, beta-cell mass and function are diminished, leading to insufficient insulin secretion and hyperglycemia.[57]
Biceps – also biceps brachii (Latin for "two-headed muscle of the arm"), is a large muscle that lies on the front of the upper arm between the shoulder and the elbow. Both heads of the muscle arise on the scapula and join to form a single muscle belly which is attached to the upper forearm. While the biceps crosses both the shoulder and elbow joints, its main function is at the elbow where it flexes the forearm and supinates the forearm. Both these movements are used when opening a bottle with a corkscrew: first biceps unscrews the cork (supination), then it pulls the cork out (flexion).[58]
Biceps brachii – The biceps, also biceps brachii (Latin for "two-headed muscle of the arm"), is a large muscle that lies on the front of the upper arm between the shoulder and the elbow. Both heads of the muscle arise on the scapula and join to form a single muscle belly which is attached to the upper forearm. While the biceps crosses both the shoulder and elbow joints, its main function is at the elbow where it flexes the forearm and supinates the forearm. Both these movements are used when opening a bottle with a corkscrew: first biceps unscrews the cork (supination), then it pulls the cork out (flexion).[58]
Bile duct – is any of a number of long tube-like structures that carry bile. Bile, required for the digestion of food, is secreted by the liver into passages that carry bile toward the hepatic duct, which joins with the cystic duct (carrying bile to and from the gallbladder) to form the common bile duct, which opens into the intestine.
Biliary tract – The biliary tract, (biliary tree or biliary system) refers to the liver, gall bladder and bile ducts, and how they work together to make, store and secrete bile. Bile consists of water, electrolytes, bile acids, cholesterol, phospholipids and conjugated bilirubin. Some components are synthesised by hepatocytes (liver cells), the rest are extracted from the blood by the liver.
Binge eating disorder – (BED), is an eating disorder characterized by frequent and recurrent binge eating episodes with associated negative psychological and social problems, but without subsequent purging episodes (e.g. vomiting). BED is a recently described condition,[59] which was required to distinguish binge eating similar to that seen in bulimia nervosa but without characteristic purging. Individuals who are diagnosed with bulimia nervosa and binge eating disorder exhibit similar patterns of compulsive overeating, neurobiological features of dysfunctional cognitive control and food addiction, and biological and environmental risk factors.[60] Indeed, some consider BED a milder version of bulimia, and that the conditions are on the same spectrum.[61]
Biological engineering – or bioengineering, or bio-engineering, is the application of principles of biology and the tools of engineering to create usable, tangible, economically viable products.[62] Biological engineering employs knowledge and expertise from a number of pure and applied sciences,[63] such as mass and heat transfer, kinetics, biocatalysts, biomechanics, bioinformatics, separation and purification processes, bioreactor design, surface science, fluid mechanics, thermodynamics, and polymer science. It is used in the design of medical devices, diagnostic equipment, biocompatible materials, renewable bioenergy, ecological engineering, agricultural engineering, and other areas that improve the living standards of societies.
Biology – is the natural science that studies life and living organisms, including their physical structure, chemical processes, molecular interactions, physiological mechanisms, development and evolution.[64]
Biochemistry – sometimes called biological chemistry, is the study of chemical processes within and relating to living organisms.[65]
Bioinformatics – is an interdisciplinary field that develops methods and software tools for understanding biological data. As an interdisciplinary field of science, bioinformatics combines biology, computer science, information engineering, mathematics and statistics to analyze and interpret biological data.
Biopsy – is a medical test commonly performed by a surgeon, interventional radiologist, or an interventional cardiologist involving extraction of sample cells or tissues for examination to determine the presence or extent of a disease.
Biostatistics – are the application of statistics to a wide range of topics in biology. It encompasses the design of biological experiments, especially in medicine, pharmacy, agriculture and fishery; the collection, summarization, and analysis of data from those experiments; and the interpretation of, and inference from, the results. A major branch is medical biostatistics, which is exclusively concerned with medicine and health.[66]
Bipolar disorder – is a mental disorder that causes periods of depression and periods of abnormally elevated mood[67][68][69]
Birth control – also known as contraception and fertility control, is a method or device used to prevent pregnancy.[70]
Bladder cancer – is any of several types of cancer arising from the tissues of the urinary bladder.[71] It is a disease in which cells grow abnormally and have the potential to spread to other parts of the body.[72][73] Symptoms include blood in the urine, pain with urination, and low back pain.[71]
Blood pressure – is the pressure of circulating blood on the walls of blood vessels. Used without further specification, "blood pressure" usually refers to the pressure in large arteries of the systemic circulation. Blood pressure is usually expressed in terms of the systolic pressure (maximum during one heartbeat) over diastolic pressure (minimum in between two heartbeats) and is measured in millimeters of mercury (mmHg), above the surrounding atmospheric pressure.
Blood vessel – The blood vessels are the part of the circulatory system, and microcirculation, that transports blood throughout the human body.[74]
Bone – is a rigid organ that constitutes part of the vertebrate skeleton. Bones support and protect the various organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and enable mobility. Bones come in a variety of shapes and sizes and have a complex internal and external structure. They are lightweight yet strong and hard, and serve multiple functions.
Bone marrow – is a semi-solid tissue which may be found within the spongy or cancellous portions of bones.[75] Bone marrow is the primary site of new blood cell production or hematopoiesis.[76] It is composed of hematopoietic cells, marrow adipose tissue, and supportive stromal cells. In adult humans, bone marrow is primarily located in the ribs, vertebrae, sternum, and bones of the pelvis.[77] On average, bone marrow constitutes 4% of the total body mass of humans; in an adult having 65 kilograms of mass (143 lb), bone marrow typically accounts for approximately 2.6 kilograms (5.7 lb).[78]
Brachial artery – is the major blood vessel of the (upper) arm. It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa at the elbow. It then divides into the radial and ulnar arteries which run down the forearm. In some individuals, the bifurcation occurs much earlier and the ulnar and radial arteries extend through the upper arm. The pulse of the brachial artery is palpable on the anterior aspect of the elbow, medial to the tendon of the biceps, and, with the use of a stethoscope and sphygmomanometer (blood pressure cuff) often used to measure the blood pressure.
Brachial plexus – is a network of nerves formed by the ventral rami of the lower four cervical nerves and first thoracic nerve (C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in the neck, over the first rib, and into the armpit. It supplies afferent and efferent nerve fibers to the chest, shoulder, arm and hand.
Brachial veins – In human anatomy, the brachial veins are venae comitantes of the brachial artery in the arm proper. Because they are deep to muscle, they are considered deep veins. Their course is that of the brachial artery (in reverse): they begin where radial veins and ulnar veins join (corresponding to the bifurcation of the brachial artery). They end at the inferior border of the teres major muscle. At this point, the brachial veins join the basilic vein to form the axillary vein. The brachial veins also have small tributaries that drain the muscles of the upper arm, such as biceps brachii muscle and triceps brachii muscle.
Brachioradialis – is a muscle of the forearm that flexes the forearm at the elbow. It is also capable of both pronation and supination, depending on the position of the forearm. It is attached to the distal styloid process of the radius by way of the brachioradialis tendon, and to the lateral supracondylar ridge of the humerus.
Bradycardia –is a condition typically defined wherein an individual has a resting heart rate of under 60 beats per minute (BPM) in adults.[79]
Brain – The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum. It controls most of the activities of the body, processing, integrating, and coordinating the information it receives from the sense organs, and making decisions as to the instructions sent to the rest of the body. The brain is contained in, and protected by, the skull bones of the head.
Brain tumor – occurs when abnormal cells form within the brain.[80] There are two main types of tumors: malignant or cancerous tumors and benign tumors.[80]
Brain metastasis – is a cancer that has metastasized (spread) to the brain from another location in the body and is therefore considered a secondary brain tumor.[81] The metastasis typically shares a cancer cell type with the original site of the cancer.[82]
Breast – The breast is one of two prominences located on the upper ventral region of the torso of primates. In females, it serves as the mammary gland, which produces and secretes milk to feed infants.[83] Both females and males develop breasts from the same embryological tissues. At puberty, estrogens, in conjunction with growth hormone, cause breast development in female humans and to a much lesser extent in other primates. Breast development in other primate females generally only occurs with pregnancy.
Breast cancer – is cancer that develops from breast tissue.[84] Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, fluid coming from the nipple, a newly inverted nipple, or a red or scaly patch of skin.[85] In those with distant spread of the disease, there may be bone pain, swollen lymph nodes, shortness of breath, or yellow skin.[86]
Broca's area – or the Broca area, is a region in the frontal lobe of the dominant hemisphere, usually the left, of the brain[87] with functions linked to speech production.
Bronchiole – The bronchioles or bronchioli are the passageways by which air passes through the nose or mouth to the alveoli (air sacs) of the lungs, in which branches no longer contain cartilage or glands in their submucosa. They are branches of the bronchi, and are part of the conducting zone of the respiratory system. The bronchioles divide further into smaller terminal bronchioles which are still in the conducting zone and these then divide into the smaller respiratory bronchioles which mark the beginning of the respiratory region.
Bronchus – A bronchi is a passage of airway in the respiratory system that conducts air into the lungs. The first bronchi to branch from the trachea are the right main bronchus and the left main bronchus. These are the widest and enter the lungs at each hilum, where they branch into narrower secondary bronchi known as lobar bronchi, and these branch into narrower tertiary bronchi known as segmental bronchi. Further divisions of the segmental bronchi are known as 4th order, 5th order, and 6th order segmental bronchi, or grouped together as subsegmental bronchi.[88][89] The bronchi when too narrow to be supported by cartilage are known as bronchioles. No gas exchange takes place in the bronchi.
Bruit – also called vascular murmur,[90] is the abnormal sound generated by turbulent flow of blood in an artery due to either an area of partial obstruction or a localized high rate of blood flow through an unobstructed artery.[91]
Bulimia nervosa – also known as simply bulimia, is an eating disorder characterized by binge eating followed by purging.[92] Binge eating refers to eating a large amount of food in a short amount of time.[92] Purging refers to the attempts to get rid of the food consumed.[92]
Buttocks – are two rounded portions of the anatomy, located on the posterior of the pelvic region and comprise a layer of fat superimposed on the gluteus maximus and gluteus medius muscles. Physiologically, the buttocks enable weight to be taken off the feet while sitting.
C
Calcium – Calcium ions (Ca2+) contribute to the physiology and biochemistry of organisms and the cell. They play an important role in signal transduction pathways,[93][94] where they act as a second messenger, in neurotransmitter release from neurons, in contraction of all muscle cell types, and in fertilization. Many enzymes require calcium ions as a cofactor, those of the blood-clotting cascade being notable examples. Extracellular calcium is also important for maintaining the potential difference across excitable cell membranes, as well as proper bone formation.
Calf – is the back portion of the lower leg in human anatomy. The muscles within the calf correspond to the posterior compartment of the leg. The two largest muscles within this compartment are known together as the calf muscle and attach to the heel via the Achilles tendon. Several other, smaller muscles attach to the knee, the ankle, and via long tendons to the toes.
Cancer – is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body.[95][96] These contrast with benign tumors, which do not spread to other parts of the body.[96]
Capillary – is a small blood vessel from 5 to 10 micrometres (µm) in diameter, and having a wall one endothelial cell thick. They are the smallest blood vessels in the body: they convey blood between the arterioles and venules. These microvessels are the site of exchange of many substances with the interstitial fluid surrounding them.
Carcinogen – is any substance, radionuclide, or radiation that promotes carcinogenesis, the formation of cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes.
Carcinogenesis – also called oncogenesis or tumorigenesis, is the formation of a cancer, whereby normal cells are transformed into cancer cells.
Cardiac arrest – a sudden loss of blood flow resulting from the failure of the heart to effectively pump.[97] Symptoms include loss of consciousness and abnormal or absent breathing.[98][99] Some individuals may experience chest pain, shortness of breath, or nausea before cardiac arrest.[99] If not treated within minutes, it typically leads to death.[97]
Cardiac catheterization – (heart cath or just cath), is the insertion of a catheter into a chamber or vessel of the heart. This is done both for diagnostic and interventional purposes.
Cardiac muscle – (also called heart muscle or myocardium), is one of three types of vertebrate muscles, with the other two being skeletal and smooth muscles. It is an involuntary, striated muscle that constitutes the main tissue of the walls of the heart. The myocardium forms a thick middle layer between the outer layer of the heart wall (the epicardium) and the inner layer (the endocardium), with blood supplied via the coronary circulation. It is composed of individual heart muscle cells (cardiomyocytes) joined together by intercalated discs, encased by collagen fibres and other substances that form the extracellular matrix.
Cardiac surgery – or cardiovascular surgery, is surgery on the heart or great vessels performed by cardiac surgeons. It is often used to treat complications of ischemic heart disease (for example, with coronary artery bypass grafting); to correct congenital heart disease; or to treat valvular heart disease from various causes, including endocarditis, rheumatic heart disease, and atherosclerosis. It also includes heart transplantation.
Cardiology – is a branch of medicine dealing with disorders of the heart as well as parts of the circulatory system.
Cardiothoracic surgery – (also known as thoracic surgery) is the field of medicine involved in surgical treatment of organs inside the thorax (the chest)—generally treatment of conditions of the heart (heart disease) and lungs (lung disease).
Cardiovascular disease – (CVD), is a class of diseases that involve the heart or blood vessels.[100] CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack).[100] Other CVDs include stroke, heart failure, hypertensive heart disease, rheumatic heart disease, cardiomyopathy, heart arrhythmia, congenital heart disease, valvular heart disease, carditis, aortic aneurysms, peripheral artery disease, thromboembolic disease, and venous thrombosis.[100][101]
Carotid artery, common – In anatomy, the left and right common carotid arteries (carotids) [102][103]) are arteries that supply the head and neck with oxygenated blood; they divide in the neck to form the external and internal carotid arteries.[104][105]
Carotid artery, external – The external carotid artery is a major artery of the head and neck. It arises from the common carotid artery when it splits into the external and internal carotid artery. It supplies blood to the face and neck.[106]
Carotid artery, internal – The internal carotid artery is a major paired artery, one on each side of the head and neck, in human anatomy. They arise from the common carotid arteries where these bifurcate into the internal and external carotid arteries at cervical vertebral level 3 or 4; the internal carotid artery supplies the brain, while the external carotid nourishes other portions of the head, such as face, scalp, skull, and meninges.
Carotid artery stenosis – is a narrowing or constriction of any part of the carotid arteries, usually caused by atherosclerosis.
Carpal bones – Are the eight small bones that make up the wrist (or carpus) that connects the hand to the forearm. In human anatomy, the main role of the wrist is to facilitate effective positioning of the hand and powerful use of the extensors and flexors of the forearm, and the mobility of individual carpal bones increase the freedom of movements at the wrist.[107]
Carpal tunnel syndrome – (CTS), is a medical condition due to compression of the median nerve as it travels through the wrist at the carpal tunnel.[108] The main symptoms are pain, numbness and tingling in the thumb, index finger, middle finger and the thumb side of the ring fingers.[108]
Cartilage – is a resilient and smooth elastic tissue, a rubber-like padding that covers and protects the ends of long bones at the joints, and is a structural component of the rib cage, the ear, the nose, the bronchial tubes, the intervertebral discs, and many other body components. It is not as hard and rigid as bone, but it is much stiffer and much less flexible than muscle. The matrix of cartilage is made up of chondrin.
Cartilaginous joint – Cartilaginous joints are connected entirely by cartilage (fibrocartilage or hyaline).[109] Cartilaginous joints allow more movement between bones than a fibrous joint but less than the highly mobile synovial joint. Cartilaginous joints also forms the growth regions of immature long bones and the intervertebral discs of the spinal column.
Catheter – Is a thin tube made from medical grade materials serving a broad range of functions. Catheters are medical devices that can be inserted in the body to treat diseases or perform a surgical procedure. By modifying the material or adjusting the way catheters are manufactured, it is possible to tailor catheters for cardiovascular, urological, gastrointestinal, neurovascular, and ophthalmic applications.
Celiac disease – another way of spelling coeliac disease
Cell biology – also called cytology, is a branch of biology that studies the structure and function of the cell, which is the basic unit of life.[110] Cell biology is concerned with the physiological properties, metabolic processes, signaling pathways, life cycle, chemical composition and interactions of the cell with their environment.
Central nervous system – (CNS), is the part of the nervous system consisting of the brain and spinal cord.
Cephalic vein – is a superficial vein in the arm.[111] It communicates with the basilic vein via the median cubital vein at the elbow and is located in the superficial fascia along the anterolateral surface of the biceps brachii muscle. Near the shoulder, the cephalic vein passes between the deltoid and pectoralis major muscles (deltopectoral groove) and through the deltopectoral triangle, where it empties into the axillary vein.
Cerebellum – (Latin for "little brain"), is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger.[112] In humans, the cerebellum plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language as well as in regulating fear and pleasure responses,[113] but its movement-related functions are the most solidly established. The human cerebellum does not initiate movement, but contributes to coordination, precision, and accurate timing: it receives input from sensory systems of the spinal cord and from other parts of the brain, and integrates these inputs to fine-tune motor activity.[114] Cerebellar damage produces disorders in fine movement, equilibrium, posture, and motor learning in humans.[114]
Cerebrum – is a large part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. In the human brain, the cerebrum is the uppermost region of the central nervous system. The prosencephalon is the embryonic structure from which the cerebrum develops prenatally. In mammals, the dorsal telencephalon, or pallium, develops into the cerebral cortex, and the ventral telencephalon, or subpallium, becomes the basal ganglia. The cerebrum is also divided into approximately symmetric left and right cerebral hemispheres. With the assistance of the cerebellum, the cerebrum controls all voluntary actions in the body.
Cervical cancer – is a cancer arising from the cervix.[85] It is due to the abnormal growth of cells that have the ability to invade or spread to other parts of the body.[115] Early on, typically no symptoms are seen.[85] Later symptoms may include abnormal vaginal bleeding, pelvic pain, or pain during sexual intercourse.[85] While bleeding after sex may not be serious, it may also indicate the presence of cervical cancer.[116]
Cervix – or cervix uteri, is the lower part of the uterus in the human female reproductive system. The cervix is usually 2 to 3 cm long (~1 inch) and roughly cylindrical in shape, which changes during pregnancy. The narrow, central cervical canal runs along its entire length, connecting the uterine cavity and the lumen of the vagina. The opening into the uterus is called the internal os, and the opening into the vagina is called the external os. The lower part of the cervix, known as the vaginal portion of the cervix (or ectocervix), bulges into the top of the vagina.
Cheek – The cheeks constitute the area of the face below the eyes and between the nose and the left or right ear. "Buccal" means relating to the cheek. In humans, the region is innervated by the buccal nerve. The area between the inside of the cheek and the teeth and gums is called the vestibule or buccal pouch or buccal cavity and forms part of the mouth.
Chin – is the area of the face below the lower lip and including the mandibular prominence.[117][118] It is formed by the lower front of the mandible.
Chronic fatigue syndrome – (CFS), also referred to as myalgic encephalomyelitis (ME), is a medical condition characterized by long-term fatigue and other persistent symptoms that limit a person's ability to carry out ordinary daily activities.[119][120]
Ciliary muscle – is a ring of smooth muscle[121][122] in the eye's middle layer (vascular layer) that controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humor into Schlemm's canal. It changes the shape of the lens within the eye, not the size of the pupil[123] which is carried out by the sphincter pupillae muscle and dilator pupillae.
Circulatory system – The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to circulate and transport nutrients (such as amino acids and electrolytes), oxygen, carbon dioxide, hormones, and blood cells to and from the cells in the body to provide nourishment and help in fighting diseases, stabilize temperature and pH, and maintain homeostasis.
Clavicle – also known as the collar bone, is a long bone that serves as a strut between the shoulder blade and the sternum. There are two, one on the right, and one on the left side of the trunk. Along with the shoulder blade, the clavicles make up the shoulder girdle. The clavicle has many functions. It connects the axial and appendicular skeleton in conjunction with the scapula, helps extend range of motion, and protects neurovascular structures.[124]
Clinic – (or outpatient clinic or ambulatory care clinic) is a healthcare facility that is primarily focused on the care of outpatients. Clinics can be privately operated or publicly managed and funded.
Clinical research – is a branch of healthcare science that determines the safety and effectiveness (efficacy) of medications, devices, diagnostic products and treatment regimens intended for human use. These may be used for prevention, treatment, diagnosis or for relieving symptoms of a disease. Clinical research is different from clinical practice. In clinical practice established treatments are used, while in clinical research evidence is collected to establish a treatment.
Coeliac disease – Coeliac disease or celiac disease is a long-term autoimmune disorder that primarily affects the small intestine.[125] Classic symptoms include gastrointestinal problems such as chronic diarrhoea, abdominal distention, malabsorption, loss of appetite and among children failure to grow normally.[126] This often begins between six months and two years of age.[126] Non-classic symptoms are more common, especially in people older than two years.[127][128][129][130] There may be mild or absent gastrointestinal symptoms, a wide number of symptoms involving any part of the body or no obvious symptoms.[126] Coeliac disease was first described in childhood;[131][127] however, it may develop at any age.[126][127] It is associated with other autoimmune diseases, such as diabetes mellitus type 1 and thyroiditis, among others.[131]
Colorectal surgery – is a field in medicine dealing with disorders of the rectum, anus, and colon.[132]
Common carotid artery – In anatomy, the left and right common carotid arteries (carotids) [102][103]) are arteries that supply the head and neck with oxygenated blood; they divide in the neck to form the external and internal carotid arteries.[104][105]
Common cold – also known simply as a cold, is a viral infectious disease of the upper respiratory tract that primarily affects the nose.[133] The throat, sinuses, and larynx may also be affected.[134] Signs and symptoms may appear less than two days after exposure to the virus.[134] These may include coughing, sore throat, runny nose, sneezing, headache, and fever.[135][136] People usually recover in seven to ten days,[137] but some symptoms may last up to three weeks.[138] Occasionally, those with other health problems may develop pneumonia.[139]
Common iliac artery – The common iliac arteries are two large arteries that originate from the aortic bifurcation at the level of the fourth lumbar vertebra. They end in front of the sacroiliac joint, one on either side, and each bifurcates into the external and internal iliac arteries.
Common iliac vein – The common iliac veins are formed by the external iliac veins and internal iliac veins. The left and right common iliac veins come together in the abdomen at the level of the fifth lumbar vertebra,[140] forming the inferior vena cava. They drain blood from the pelvis and lower limbs. Both common iliac veins are accompanied along their course by common iliac arteries.
Coronary arteries – are the blood vessels (arteries) of coronary circulation, which transports oxygenated blood to the actual heart muscle. The heart requires a continuous supply of oxygen to function and survive, much like any other tissue or organ of the body.[141]
Corpus callosum – also callosal commissure, is a wide, thick nerve tract consisting of a flat bundle of commissural fibers, beneath the cerebral cortex in the brain. The corpus callosum is only found in placental mammals.[142] It spans part of the longitudinal fissure, connecting the left and right cerebral hemispheres, enabling communication between them. It is the largest white matter structure in the human brain, about ten centimetres in length and consisting of 200–300 million axonal projections.[143][144]
Cranial nerves – are the nerves that emerge directly from the brain (including the brainstem), in contrast to spinal nerves (which emerge from segments of the spinal cord).[145] Ten of the cranial nerves originate in the brainstem. Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck.[146]
Cure – is a substance or procedure that ends a medical condition, such as a medication, a surgical operation, a change in lifestyle or even a philosophical mindset that helps end a person's sufferings; or the state of being healed, or cured.
Cytogenetics – is a branch of genetics that is concerned with how the chromosomes relate to cell behaviour, particularly to their behaviour during mitosis and meiosis.[147]
Cytokines – are a broad and loose category of small proteins (~5–20 kDa) that are important in cell signaling. Cytokines are peptides, and cannot cross the lipid bilayer of cells to enter the cytoplasm.
D
Deep circumflex iliac vein – is formed by the union of the venae comitantes of the deep iliac circumflex artery, and joins the external iliac vein about 2 cm. above the inguinal ligament. It also receives small tributary branches from the thoracoepigastric vein[148]
Deep temporal arteries – The deep temporal arteries, two in number, anterior and posterior, ascend between the temporalis and the pericranium. They supply the muscle, and anastomose with the middle temporal artery. The anterior communicates with the lacrimal artery by means of small branches which perforate the zygomatic bone and great wing of the sphenoid.
Deltoid muscle – is the muscle forming the rounded contour of the human shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the nervous system.[149]
Dentistry – also known as Dental and Oral Medicine, is a branch of medicine that consists of the study, diagnosis, prevention, and treatment of diseases, disorders, and conditions of the oral cavity, commonly in the dentition but also the oral mucosa, and of adjacent and related structures and tissues, particularly in the maxillofacial (jaw and facial) area.[150]
Dermatitis – also known as eczema, is a group of diseases that result in inflammation of the skin.[151] These diseases are characterized by itchiness, red skin and a rash.[151] In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened.[151] The area of skin involved can vary from small to the entire body.[151][152]
Diagnosis – Medical diagnosis (abbreviated Dx[153] or DS) is the process of determining which disease or condition explains a person's symptoms and signs. It is most often referred to as diagnosis with the medical context being implicit. The information required for diagnosis is typically collected from a history and physical examination of the person seeking medical care. Often, one or more diagnostic procedures, such as medical tests, are also done during the process. Sometimes posthumous diagnosis is considered a kind of medical diagnosis.
Diabetes mellitus – (DM), commonly known as diabetes, is a group of metabolic disorders characterized by a high blood sugar level over a prolonged period.[154] Symptoms of high blood sugar include frequent urination, increased thirst, and increased hunger.[155] If left untreated, diabetes can cause many complications.[155] Acute complications can include diabetic ketoacidosis, hyperosmolar hyperglycemic state, or death.[156] Serious long-term complications include cardiovascular disease, stroke, chronic kidney disease, foot ulcers, and damage to the eyes.[155]
Dietary reference intake – (DRI), is a system of nutrition recommendations from the Institute of Medicine (IOM) of the National Academies (United States).[157]
Differential diagnosis – is the distinguishing of a particular disease or condition from others that present similar clinical features.[158]
Digestive system – The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller components, until they can be absorbed and assimilated into the body.
Disease – is an abnormal condition in an organism, or part of it, that negatively affects structure or function. Disease can be caused by external factors, or internal dysfunctions, such as abnormal immune responses.
E
Ear – is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear, the middle ear and the inner ear. The outer ear consists of the pinna and the ear canal. Since the outer ear is the only visible portion of the ear in most animals, the word "ear" often refers to the external part alone.[159] The middle ear includes the tympanic cavity and the three ossicles. The inner ear sits in the bony labyrinth, and contains structures which are key to several senses: the semicircular canals, which enable balance and eye tracking when moving; the utricle and saccule, which enable balance when stationary; and the cochlea, which enables hearing. The ears of vertebrates are placed somewhat symmetrically on either side of the head, an arrangement that aids sound localisation.
Ear infection –
Elbow – is the visible joint between the upper and lower parts of the arm. It includes prominent landmarks such as the olecranon, the elbow pit, the lateral and medial epicondyles, and the elbow joint. The elbow joint[160] is the synovial hinge joint[161] between the humerus in the upper arm and the radius and ulna in the forearm which allows the forearm and hand to be moved towards and away from the body.[162]
Embryology – is the branch of biology that studies the prenatal development of gametes (sex cells), fertilization, and development of embryos and fetuses. Additionally, embryology encompasses the study of congenital disorders that occur before birth, known as teratology.[163]
Emergency medicine – also known as accident and emergency medicine, is the medical specialty concerned with the care of illnesses or injuries requiring immediate medical attention. Emergency physicians care for unscheduled and undifferentiated patients of all ages. As first-line providers, their primary responsibility is to initiate resuscitation and stabilization and to start investigations and interventions to diagnose and treat illnesses in the acute phase.
Endocrine system – is a chemical messenger system comprising feedback loops of hormones released by internal glands of an organism directly into the circulatory system, regulating distant target organs. In humans, the major endocrine glands are the thyroid gland and the adrenal glands. In vertebrates, the hypothalamus is the neural control center for all endocrine systems. The study of the endocrine system and its disorders is known as endocrinology. Endocrinology is a branch of internal medicine.[164]
Endocrinology – is a branch of biology and medicine dealing with the endocrine system, its diseases, and its specific secretions known as hormones. It is also concerned with the integration of developmental events proliferation, growth, and differentiation, and the psychological or behavioral activities of metabolism, growth and development, tissue function, sleep, digestion, respiration, excretion, mood, stress, lactation, movement, reproduction, and sensory perception caused by hormones. Specializations include behavioral endocrinology[165][166][167] and comparative endocrinology.
Epidemiology – is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in defined populations. It is a cornerstone of public health, and shapes policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive healthcare. Epidemiologists help with study design, collection, and statistical analysis of data, amend interpretation and dissemination of results (including peer review and occasional systematic review). Epidemiology has helped develop methodology used in clinical research, public health studies, and, to a lesser extent, basic research in the biological sciences.[168]
Epiglottis – is a leaf-shaped flap in the throat that prevents food from entering the windpipe and the lungs. It stands open during breathing, allowing air into the larynx. During swallowing, it closes to prevent aspiration of food into the lungs, forcing the swallowed liquids or food to go along the esophagus toward the stomach instead. It is thus the valve that diverts passage to either the trachea or the esophagus.
Epilepsy – is a group of neurological disorders characterized by recurrent epileptic seizures.[169][170] Epileptic seizures are episodes that can vary from brief and nearly undetectable periods to long periods of vigorous shaking.[171] These episodes can result in physical injuries, including occasionally broken bones.[172] In epilepsy, seizures have a tendency to recur and, as a rule, have no immediate underlying cause.[169] Isolated seizures that are provoked by a specific cause such as poisoning are not deemed to represent epilepsy.[173]
Erectile dysfunction –
Erector spinae muscles –
Esophagus – The esophagus, (American English) or oesophagus (British English; see spelling differences) (/ɪˈsɒfəɡəs/), informally known as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the stomach. The esophagus is a fibromuscular tube, about 25 cm (10 in) long in adults, which travels behind the trachea and heart, passes through the diaphragm and empties into the uppermost region of the stomach. During swallowing, the epiglottis tilts backwards to prevent food from going down the larynx and lungs.
Extensor pollicis brevis muscle –
Extensor pollicis et indicis communis muscle –
Extensor pollicis longus muscle –
External carotid artery –
External iliac artery –
External iliac vein –
External jugular vein –
Eye –
Eye surgery –
F
Face – is the front of an animal's head that features three of the head's sense organs, the eyes, nose, and mouth, and through which animals express many of their emotions.[174][175] The face is crucial for human identity, and damage such as scarring or developmental deformities affects the psyche adversely.[174]
Fallopian tube – The Fallopian tubes, also known as uterine tubes or salpinges (singular salpinx), are tubes that stretch from the uterus to the ovaries, and are part of the female reproductive system. The fertilized egg passes through the Fallopian tubes from the ovaries of female mammals to the uterus. The Fallopian tubes is simple columnar epithelium with hair-like extensions called cilia which carry the fertilized egg. In other animals, the equivalent of a Fallopian tube is an oviduct.
Fellowship (medicine) – is the period of medical training, in the United States and Canada, that a physician, dentist, or veterinarian may undertake after completing a specialty training program (residency). During this time (usually more than one year), the physician is known as a fellow. Fellows are capable of acting as an attending physician or a consultant physician in the specialist field in which they were trained, such as Internal Medicine or Pediatrics. After completing a fellowship in the relevant sub-specialty, the physician is permitted to practice without direct supervision by other physicians in that sub-specialty, such as Cardiology or Oncology.
Female reproductive system – is made up of the internal and external sex organs that function in reproduction of new offspring. In humans, the female reproductive system is immature at birth and develops to maturity at puberty to be able to produce gametes, and to carry a foetus to full term. The internal sex organs are the uterus, Fallopian tubes, and ovaries. The uterus or womb accommodates the embryo which develops into the foetus. The uterus also produces vaginal and uterine secretions which help the transit of sperm to the Fallopian tubes. The ovaries produce the ova (egg cells). The external sex organs are also known as the genitals and these are the organs of the vulva including the labia, clitoris, and vaginal opening. The vagina is connected to the uterus at the cervix.[176]
Femoral artery – is a large artery in the thigh and the main arterial supply to the thigh and leg. It enters the thigh from behind the inguinal ligament as the continuation of the external iliac artery.
Femoral nerve – is a nerve in the thigh that supplies skin on the upper thigh and inner leg, and the muscles that extend the knee.
Femoral vein – In the human body, the femoral vein is a blood vessel that accompanies the femoral artery in the femoral sheath. It begins at the adductor hiatus (an opening in the adductor magnus muscle) and is a continuation of the popliteal vein. It ends at the inferior margin of the inguinal ligament, where it becomes the external iliac vein. The femoral vein bears valves which are mostly bicuspid and whose number is variable between individuals and often between left and right leg.[177]
Femur – The femur, or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrate, the largest bone of the human body. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with the tibia and kneecap, forming the knee joint.
Fibromyalgia –
Fibrous joint –
Fibula –
Finger –
First aid –
Flat bone –
Foot –
Forearm –
Forehead –
Frontal bone –
Frontal nerve –
Frontalis muscle –
G
Gallbladder – In vertebrates, the gallbladder is a small hollow organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath the liver, although the structure and position of the gallbladder can vary significantly among animal species. It receives and stores bile, produced by the liver, via the common hepatic duct and releases it via the common bile duct into the duodenum, where the bile helps in the digestion of fats.
Gamete –
Ganglion – is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympathetic and parasympathetic ganglia which contain the cell bodies of postganglionic sympathetic and parasympathetic neurons respectively.
Gastrocnemius muscle – (plural gastrocnemii) is a superficial two-headed muscle that is in the back part of the lower leg of humans. It runs from its two heads just above the knee to the heel, a three joint muscle (knee, ankle and subtalar joints). The muscle is named via Latin, from Greek γαστήρ (gaster) 'belly' or 'stomach' and κνήμη (knḗmē) 'leg', meaning 'stomach of leg' (referring to the bulging shape of the calf).
Gastroenterology –
Gastrointestinal tract –
Gene therapy –
General surgery –
Genetics –
Genitourinary system –
Geriatrics –
Gonad –
Gout – is a form of inflammatory arthritis characterized by recurrent attacks of a red, tender, hot, and swollen joint.[178][179] Pain typically comes on rapidly, reaching maximal intensity in less than 12 hours.[180] The joint at the base of the big toe is affected in about half of cases.[181] It may also result in tophi, kidney stones, or urate nephropathy.[180]
Gracilis muscle –
Great saphenous vein –
Gynaecology –
H
Hand – A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates. The human hand normally has five digits: four fingers plus one thumb;[182][183] these are often referred to collectively as five fingers, however, whereby the thumb is included as one of the fingers.[182][184][185] It has 27 bones, not including sesmoid bones, the number of which varies between people,[186] 14 of which are the phalanges (proximal, intermediate and distal) of the fingers and thumb. The metacarpal bones connect the fingers and the carpal bones of the wrist. Each human hand has five metacarpals[187] and eight carpal bones.
Hand surgery –
Head –
Health – as defined by the World Health Organization (WHO), is "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity."[188][189] This definition has been subject to controversy, as it may have limited value for implementation.[190][191][192] Health may be defined as the ability to adapt and manage physical, mental and social challenges throughout life.[193]
Health care – Health care, health-care, or healthcare is the maintenance or improvement of health via the prevention, diagnosis, treatment, recovery, or cure of disease, illness, injury, and other physical and mental impairments in people. Health care is delivered by health professionals and allied health fields. Physicians and physician associates are a part of these health professionals. Dentistry, pharmacy, midwifery, nursing, medicine, optometry, audiology, psychology, occupational therapy, physical therapy, athletic training and other health professions are all part of health care. It includes work done in providing primary care, secondary care, and tertiary care, as well as in public health.
Hearing –
Heart –
Heel –
Hematemesis-
Hematology –
Hematoma-
Hematuria-
Hemodialysis-
Hemolysis-
Hemopathy-
Hemoperfusion-
Hemophilia-
Hemoptysis-
Hemorrhoid-
Hyperhydrosis-
High blood pressure –
Hyperkalemia-
Hip bone –
Histology –
Homeostasis –
Hormone –
Hospice –
Hospital –
Hospital medicine –
Human back –
Human body –
Human brain –
Human digestive system –
Human eye –
Human head –
Human mouth –
Human musculoskeletal system –
Human nose –
Human reproductive system –
Human skeleton –
Humerus –
Hypersalivation –
Hypertension –
I
Iliac artery, common – The common iliac arteries are two large arteries that originate from the aortic bifurcation at the level of the fourth lumbar vertebra. They end in front of the sacroiliac joint, one on either side, and each bifurcates into the external and internal iliac arteries.
Iliac artery, external – The external iliac arteries are two major arteries which bifurcate off the common iliac arteries anterior to the sacroiliac joint of the pelvis. They proceed anterior and inferior along the medial border of the psoas major muscles. They exit the pelvic girdle posterior and inferior to the inguinal ligament about one third laterally from the insertion point of the inguinal ligament on the pubic tubercle at which point they are referred to as the femoral arteries.[194] The external iliac artery is usually the artery used to attach the renal artery to the recipient of a kidney transplant.
Ilium – (plural ilia), is the uppermost and largest part of the hip bone, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.[195] The ilium of the human is divisible into two parts, the body and the wing; the separation is indicated on the top surface by a curved line, the arcuate line, and on the external surface by the margin of the acetabulum.
Immune system – is a network of biological processes that protects an organism against disease. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as objects such as wood splinters, distinguishing them from the organism's own healthy tissue. Many species have two major subsystems of the immune system. The innate immune system provides a preconfigured response to broad groups of situations and stimuli. The adaptive immune system provides a tailored response to each stimulus by learning to recognize molecules it has previously encountered. Both use molecules and cells to perform their functions.
Immunohistochemistry –
Immunology – is a branch of biology[196] that covers the study of immune systems[197] in all organisms.[198] Immunology charts, measures, and contextualizes the physiological functioning of the immune system in states of both health and diseases; malfunctions of the immune system in immunological disorders (such as autoimmune diseases,[199] hypersensitivities,[200] immune deficiency,[201] and transplant rejection[202]); and the physical, chemical, and physiological characteristics of the components of the immune system in vitro,[203] in situ, and in vivo.[204] Immunology has applications in numerous disciplines of medicine, particularly in the fields of organ transplantation, oncology, rheumatology, virology, bacteriology, parasitology, psychiatry, and dermatology.
Iliac vein, common –
Iliac vein, deep circumflex –
Iliac vein, external –
Iliac vein, internal –
Index finger –
Infectious disease (medical specialty) –
Inferior oblique muscle –
Inferior thyroid artery –
Inferior vena cava –
Influenza –
Inspection (medicine) –
Integumentary system –
Intensive care medicine –
Internal carotid artery –
Internal iliac vein –
Internal jugular vein –
Internal medicine –
Internship (medicine) –
Interventional cardiology –
Interventional radiology –
Ischium –
J
Jaundice- also known as icterus, is a yellowish or greenish pigmentation of the skin and whites of the eyes due to high bilirubin levels.[205][206] It is commonly associated with itchiness.[207] The feces may be pale and the urine dark.[208] Jaundice in babies occurs in over half in the first week following birth and does not pose a serious threat in most.[205][206] If bilirubin levels in babies are very high for too long, a type of brain damage, known as kernicterus, may occur.[209]
Jaw – The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of humans and most animals.
Jejunum- is the second part of the small intestine in humans and most higher vertebrates, including mammals, reptiles, and birds. Its lining is specialised for the absorption by enterocytes of small nutrient molecules which have been previously digested by enzymes in the duodenum.
Joint – A joint or articulation (or articular surface) is the connection made between bones in the body which link the skeletal system into a functional whole.[210][211][212] They are constructed to allow for different degrees and types of movement. Some joints, such as the knee, elbow, and shoulder, are self-lubricating, almost frictionless, and are able to withstand compression and maintain heavy loads while still executing smooth and precise movements.[212] Other joints such as sutures between the bones of the skull permit very little movement (only during birth) in order to protect the brain and the sense organs.[212] The connection between a tooth and the jawbone is also called a joint, and is described as a fibrous joint known as a gomphosis. Joints are classified both structurally and functionally.[213]
Jugular vein – The jugular veins are veins that take deoxygenated blood from the head back to the heart via the superior vena cava.
K
Keratogenesis-
Keratopathy-
Kidney – The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about 12 centimetres (4 1⁄2 inches) in length.[214][215] They receive blood from the paired renal arteries; blood exits into the paired renal veins. Each kidney is attached to a ureter, a tube that carries excreted urine to the bladder.
Knee – In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint).[216] It is the largest joint in the human body.[217] The knee is a modified hinge joint, which permits flexion and extension as well as slight internal and external rotation. The knee is vulnerable to injury and to the development of osteoarthritis.
Korsakoff syndrome- (KS)[218] is an amnestic disorder caused by thiamine (vitamin B1) deficiency typically associated with prolonged use of alcohol.[219] The syndrome and psychosis are named after Sergei Korsakoff, the Russian neuropsychiatrist who discovered it during the late 19th century. This neurological disorder is caused by a lack of thiamine in the brain, and is also exacerbated by the neurotoxic effects of alcohol. When Wernicke encephalopathy accompanies Korsakoff syndrome the combination is called Wernicke–Korsakoff syndrome; however, a recognized episode of Wernicke encephalopathy is not always obvious.
L
Large intestine –The large intestine, also known as the large bowel or colon, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remaining waste material is stored as feces before being removed by defecation.[220]
Laryngeal prominence – The Adam's apple, or laryngeal prominence, colloquially known as the neck triangle, is the lump or protrusion in the human neck formed by the angle of the thyroid cartilage surrounding the larynx seen especially in males.
Laryngeal ventricle –
Ligament –
Lip –
Little finger –
Liver –
Long bone –
Lumbar vertebrae –
Lung –
Lung cancer –
Lupus erythematosus –
Lymph –
Lymphatic system –
Lymphatic vessel –
Lymph node –
Lymphocyte –
Lymphoma - Cancer of the lymphatic system.
M
Major depressive disorder – (MDD), also known simply as depression, is a mental disorder characterized by at least two weeks of pervasive low mood. Low self-esteem, loss of interest in normally enjoyable activities, low energy, and pain without a clear cause are common symptoms.[221] Those affected may also occasionally have delusions or hallucinations.[222] Some people have periods of depression separated by years, while others nearly always have symptoms present.[223] Major depression is more severe and lasts longer than sadness, which is a normal part of life.[224]
Male reproductive system –
Mammary gland –
Mandible – The mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human face.[225] It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone of the skull (discounting the ossicles of the middle ear).[226]
Masseter muscle – In human anatomy, the masseter is one of the muscles of mastication. Found only in mammals, it is particularly powerful in herbivores to facilitate chewing of plant matter.[227] The most obvious muscle of mastication is the masseter muscle, since it is the most superficial and one of the strongest.
Maternal-fetal medicine –
Maxilla –
MCAT – Medical College Admission Test.
Medical biology –
Medical classification – A medical classification is a list of standardized codes used in the process of medical coding and medical billing.
Medical coding – The practice of assigning statistical codes to medical statements, such as those made during a hospital stay. Closely related to medical billing.
Medical College Admission Test –
Medical device –
Medical diagnosis –
Medical ethics –
Medical history –
Medical imaging –
Medical laboratory –
Medical research –
Medical school –
Medical sign –
Medical speciality –
Medication –
Medulla oblongata –
Metacarpal bones –
Metatarsal bones –
Microbiology –
Middle finger –
Middle temporal artery –
Molecular biology –
Mouth –
Muscle –
Muscular system –
Musculoskeletal system –
N
Nail – A nail is a claw-like keratinous plate at the tip of the fingers and toes in most primates. Nails correspond to claws found in other animals. Fingernails and toenails are made of a tough protective protein called alpha-keratin which is found in the hooves, hair, claws and horns of vertebrates.[228]
Nanobiotechnology – Nanobiotechnology, bionanotechnology, and nanobiology are terms that refer to the intersection of nanotechnology and biology.[229] Given that the subject is one that has only emerged very recently, bionanotechnology and nanobiotechnology serve as blanket terms for various related technologies.
Nasal cavity – is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities,[230] also known as fossae.[231] Each cavity is the continuation of one of the two nostrils. The nasal cavity is the uppermost part of the respiratory system and provides the nasal passage for inhaled air from the nostrils to the nasopharynx and rest of the respiratory tract. The paranasal sinuses surround and drain into the nasal cavity.
Nasopharynx – The upper portion of the pharynx, the nasopharynx, extends from the base of the skull to the upper surface of the soft palate.[232] It includes the space between the internal nares and the soft palate and lies above the oral cavity. The adenoids, also known as the pharyngeal tonsils, are lymphoid tissue structures located in the posterior wall of the nasopharynx. Waldeyer's tonsillar ring is an annular arrangement of lymphoid tissue in both the nasopharynx and oropharynx. The nasopharynx is lined by respiratory epithelium that is pseudostratified, columnar, and ciliated.
Navel – The navel (clinically known as the umbilicus, colloquially known as the belly button) is a protruding, flat, or hollowed area on the abdomen at the attachment site of the umbilical cord.[233] All placental mammals have a navel.
Nephrology – is a specialty of medicine that concerns with study of the kidneys, specifically normal kidney function and kidney disease, the preservation of kidney health, and the treatment of kidney disease, from diet and medication to renal replacement therapy (dialysis and kidney transplantation).
Nerve – is an enclosed, cable-like bundle of nerve fibres called axons, in the peripheral nervous system. A nerve transmits electrical impulses and is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called action potentials that are transmitted along each of the axons to peripheral organs or, in the case of sensory nerves, from the periphery back to the central nervous system. Each axon within the nerve is an extension of an individual neuron, along with other supportive cells such as some Schwann cells that coat the axons in myelin.
Nervous system – is a highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes that impact the body, then works in tandem with the endocrine system to respond to such events.[234]
Neurology – is a branch of medicine dealing with disorders of the nervous system. Neurology deals with the diagnosis and treatment of all categories of conditions and disease involving the central and peripheral nervous systems (and their subdivisions, the autonomic and somatic nervous systems), including their coverings, blood vessels, and all effector tissue, such as muscle.[235] Neurological practice relies heavily on the field of neuroscience, the scientific study of the nervous system.
Neuroscience – (or neurobiology), is the scientific study of the nervous system.[236] It is a multidisciplinary science that combines physiology, anatomy, molecular biology, developmental biology, cytology, mathematical modeling, and psychology to understand the fundamental and emergent properties of neurons and neural circuits.[237][238][239][240][241]
Neurosurgery – or neurological surgery, is the medical specialty concerned with the prevention, diagnosis, surgical treatment, and rehabilitation of disorders which affect any portion of the nervous system including the brain, spinal cord, central and peripheral nervous system, and cerebrovascular system.[242]
Nose – The human nose is the most protruding part of the face. It bears the nostrils and is the first organ of the respiratory system. It is also the principal organ in the olfactory system. The shape of the nose is determined by the nasal bones and the nasal cartilages, including the nasal septum which separates the nostrils and divides the nasal cavity into two. On average the nose of a male is larger than that of a female.
Nuclear medicine – is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear medicine imaging, in a sense, is "radiology done inside out" or "endoradiology" because it records radiation emitting from within the body rather than radiation that is generated by external sources like X-rays. In addition, nuclear medicine scans differ from radiology, as the emphasis is not on imaging anatomy, but on the function. For such reason, it is called a physiological imaging modality. Single photon emission computed tomography (SPECT) and positron emission tomography (PET) scans are the two most common imaging modalities in nuclear medicine.[243]
Nutrition – is the science that interprets the nutrients and other substances in food in relation to maintenance, growth, reproduction, health and disease of an organism. It includes ingestion, absorption, assimilation, biosynthesis, catabolism and excretion.[244]
O
Oblique muscle of auricle – The oblique muscle of auricle (oblique auricular muscle or Tod muscle[245]) is an intrinsic muscle of the outer ear. The oblique muscle of auricle is placed on the cranial surface of the pinna. It consists of a few fibers extending from the upper and back part of the concha to the convexity immediately above it.[246]
Obstetrics – is the field of study concentrated on pregnancy, childbirth and the postpartum period. As a medical specialty, obstetrics is combined with gynecology under the discipline known as obstetrics and gynecology (OB/GYN), which is a surgical field.[247]
Obstetrics and gynaecology – Obstetrics and gynaecology (British English) or obstetrics and gynecology (American English) is the medical specialty that encompasses the two subspecialties of obstetrics (covering pregnancy, childbirth, and the postpartum period) and gynecology (covering the health of the female reproductive system – vagina, uterus, ovaries, and breasts). It is commonly abbreviated as OB-GYN or OB/GYN in US English, and as obs and gynae or O&G in British English.
Occipital bone – is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cerebrum. At the base of skull in the occipital bone, there is a large oval opening called the foramen magnum, which allows the passage of the spinal cord.
Ocular surgery –
Olfaction – or the sense of smell,[248] is the process of creating the perception of smell.[249] It occurs when an odor binds to a receptor within the nose, transmitting a signal through the olfactory system. Olfaction has many purposes, including detecting hazards, pheromones, and plays a role in taste.
Oncology – is a branch of medicine that deals with the prevention, diagnosis, and treatment of cancer. A medical professional who practices oncology is an oncologist.[250]
Ophthalmology –
Optometry –
Organ –
Oral and maxillofacial surgery –
Orbicularis oculi muscle –
Orbicularis oris muscle –
Orthopedic surgery –
Ossicles –
Otitis –
Otorhinolaryngology –
Ovary –
P
Palate – is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity.[251] A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly separated. The palate is divided into two parts, the anterior, bony hard palate and the posterior, fleshy soft palate (or velum).[252][253]
Palliative care – (derived from the Latin root palliare, or "to cloak") is an interdisciplinary medical caregiving approach aimed at optimizing quality of life and mitigating suffering among people with serious, complex illness.[254] Within the published literature, many definitions of palliative care exist; most notably, the World Health Organization describes palliative care as "an approach that improves the quality of life of patients and their families facing the problems associated with life-threatening illness, through the prevention and relief of suffering by means of early identification and impeccable assessment and treatment of pain and other problems, physical, psychosocial, and spiritual."[255] In the past, palliative care was a disease specific approach, but today the World Health Organization takes a more broad approach, that the principles of palliative care should be applied as early as possible to any chronic and ultimately fatal illness.[256]
Palpation – is the process of using one's hands to check the body, especially while perceiving/diagnosing a disease or illness.[257]
Pancreas – is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas has both an endocrine and a digestive exocrine function. As an endocrine gland, it functions mostly to regulate blood sugar levels, secreting the hormones insulin, glucagon, somatostatin, and pancreatic polypeptide. As a part of the digestive system, it functions as an exocrine gland secreting pancreatic juice into the duodenum through the pancreatic duct. This juice contains bicarbonate, which neutralizes acid entering the duodenum from the stomach; and digestive enzymes, which break down carbohydrates, proteins, and fats in food entering the duodenum from the stomach.
Papillary - In oncology, papillary refers to neoplasms with projections ("papillae", from Latin, 'nipple') that have fibrovascular cores.
Parasitology – is the study of parasites, their hosts, and the relationship between them. As a biological discipline, the scope of parasitology is not determined by the organism or environment in question but by their way of life. This means it forms a synthesis of other disciplines, and draws on techniques from fields such as cell biology, bioinformatics, biochemistry, molecular biology, immunology, genetics, evolution and ecology.
Parathyroid gland –
Parkinson's disease –
Patella –
Pathology –
Pectineus muscle –
Pectoralis major muscle –
Pectoralis minor muscle –
Pediatrics –
Pelvis –
Penis –
Percussion (medicine) –
Peripheral nervous system –
Peripheral vision –
Phalanx bone –
Pharmacology –
Pharynx –
Physician –
Physical examination –
Physiology –
Pineal gland –
Pituitary gland –
Placenta –
Plastic surgery –
Plexus – A branching network of vessels or nerves.
Pons –
Posterior tibial artery –
Preventive healthcare –
Prognosis –
Prostate –
Psychiatry –
Pubis –
Pulmonary artery –
Pulmonary circulation –
Pulmonary vein –
Pulmonology –
Pulse –
Q
Quadriplegia – Tetraplegia, also known as quadriplegia, is paralysis caused by illness or injury that results in the partial or total loss of use of all four limbs and torso; paraplegia is similar but does not affect the arms. The loss is usually sensory and motor, which means that both sensation and control are lost. The paralysis may be flaccid or spastic.
R
Radial artery – In human anatomy, the radial artery is the main artery of the lateral aspect of the forearm.
Radial nerve – is a nerve in the human body that supplies the posterior portion of the upper limb. It innervates the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm and the associated joints and overlying skin. It originates from the brachial plexus, carrying fibers from the ventral roots of spinal nerves C5, C6, C7, C8 & T1.[258]
Radiology – is the medical discipline that uses medical imaging to diagnose and treat diseases within the body.
Radius – The radius, or radial bone, is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna. The ulna is usually slightly longer than the radius, but the radius is thicker. Therefore the radius is considered to be the larger of the two. It is a long bone, prism-shaped and slightly curved longitudinally.
Rectum –
Rectus abdominis muscle –
Rectus femoris muscle –
Red blood cell – The most common type of blood cell and the vertebrate's principal means of delivering oxygen to the body tissues — via blood flow through the circulatory system. Red blood cells take up oxygen in the lungs and release it into tissues while squeezing through the body's capillaries.
Renal artery –
Renal vein –
Reproductive system –
Residency (medicine) –
Respiratory system –
Rheumatology –
Rib cage –
Ring finger –
S
Sacrum – The sacrum (plural: sacra or sacrums[259]), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of sacral vertebrae S1–S5 between 18 and 30 years of age.[260]
Salivary gland – The salivary glands in mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands (parotid, submandibular, and sublingual), a pair of seromucous tubarial glands (discovered in 2020) as well as hundreds of minor salivary glands.[261] Salivary glands can be classified as serous, mucous or seromucous (mixed).
Saphenous nerve – (long or internal saphenous nerve) is the largest cutaneous branch of the femoral nerve. It is a strictly sensory nerve, and has no motor function.
Saphenous vein, great –
Saphenous vein, small –
Sartorius muscle –
Scalp –
Scapula –
Sciatic nerve –
Scrotum –
Sebaceous gland –
Seminal vesicle –
Sensory nervous system –
Sensory processing –
Serratus anterior muscle –
Serratus posterior inferior muscle –
Serratus posterior superior muscle –
Skeletal muscle –
Skin –
Skull –
Small intestine –
Small saphenous vein –
Smooth muscle tissue –
Special senses –
Specialty (medicine) –
Spinal cord –
Spinal nerve –
Sole –
Soleus muscle –
Spleen –
Sports medicine –
Sternohyoid muscle –
Sternum –
Stomach –
Striated muscle tissue –
Subclavian artery –
Subcutaneous tissue –
Superficial temporal artery –
Superior oblique muscle –
Superior thyroid artery –
Superior vena cava –
Surgery –
Sweat gland –
Symptom –
Synovial bursa –
Synovial joint –
Synovial membrane –
Systemic lupus erythematosus –
Systems biology –
T
Tarsus – In the human body, the tarsus is a cluster of seven articulating bones in each foot situated between the lower end of the tibia and the fibula of the lower leg and the metatarsus. It is made up of the midfoot (cuboid, medial, intermediate, and lateral cuneiform, and navicular) and hindfoot (talus and calcaneus).
Taste – The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor).[262] Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor cells located on taste buds in the oral cavity, mostly on the tongue. Taste, along with smell (olfaction) and trigeminal nerve stimulation (registering texture, pain, and temperature), determines flavors of food and other substances. Humans have taste receptors on taste buds and other areas including the upper surface of the tongue and the epiglottis.[263][264] The gustatory cortex is responsible for the perception of taste.
Teeth –
Temple –
Temporal arteries, deep –
Temporal artery, middle –
Temporal artery, superficial –
Temporal muscle –
Tendon –
Tensor fasciae latae muscle –
Testicle –
Thigh –
Thoracic diaphragm –
Thorax –
Throat –
Thumb –
Thymus –
Thyroid –
Thyroid artery, inferior –
Thyroid artery, superior –
Thyroid ima artery –
Tibia –
Tibialis anterior muscle –
Tibialis posterior muscle –
Tissue –
Toe –
Toll-like receptor –
Tongue –
Toxicology –
Trachea –
Trapezius muscle –
Triceps brachii muscle –
U
Ulna – is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. It runs parallel to the radius, the other long bone in the forearm. The ulna is usually slightly longer than the radius, but the radius is thicker. Therefore the radius is considered to be the larger of the two.
Ulnar artery – is the main blood vessel, with oxygenated blood, of the medial aspects of the forearm. It arises from the brachial artery and terminates in the superficial palmar arch, which joins with the superficial branch of the radial artery. It is palpable on the anterior and medial aspect of the wrist.
Ulnar nerve – In human anatomy, the ulnar nerve is a nerve that runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest in the human body unprotected by muscle or bone, so injury is common.[265] This nerve is directly connected to the little finger, and the adjacent half of the ring finger, innervating the palmar aspect of these fingers, including both front and back of the tips, perhaps as far back as the fingernail beds.
Ureter – The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In the human adult, the ureters are usually 20–30 cm (8–12 in) long and around 3–4 mm (0.12–0.16 in) in diameter. The ureter is lined by urothelial cells, a type of transitional epithelium, and has an additional smooth muscle layer in third closest to the bladder that assists with peristalsis.
Urethra – The urethra is a tube that connects the urinary bladder to the urinary meatus for the removal of urine from the body of both females and males. In human females and other primates, the urethra connects to the urinary meatus above the vagina, whereas in marsupials, the female's urethra empties into the urogenital sinus.[266] Females use their urethra only for urinating, but males use their urethra for both urination and ejaculation.[267] The external urethral sphincter is a striated muscle that allows voluntary control over urination.[268] The internal sphincter, formed by the involuntary smooth muscles lining the bladder neck and urethra, receives its nerve supply by the sympathetic division of the autonomic nervous system.[269] The internal sphincter is present both in males and females.[270][271][272]
Urinary bladder – The urinary bladder, or simply bladder, is a hollow muscular organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In the human the bladder is a hollow muscular, and distensible organ that sits on the pelvic floor. Urine enters the bladder via the ureters and exits via the urethra. The typical human bladder will hold between 300 and 500 ml (10.14 and 16.91 fl oz) before the urge to empty occurs, but can hold considerably more.[273][274]
Urinary system – The urinary system, also known as the renal system or urinary tract, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, control levels of electrolytes and metabolites, and regulate blood pH. The urinary tract is the body's drainage system for the eventual removal of urine.[275] The kidneys have an extensive blood supply via the renal arteries which leave the kidneys via the renal vein. Each kidney consists of functional units called nephrons. Following filtration of blood and further processing, wastes (in the form of urine) exit the kidney via the ureters, tubes made of smooth muscle fibres that propel urine towards the urinary bladder, where it is stored and subsequently expelled from the body by urination (voiding). The female and male urinary system are very similar, differing only in the length of the urethra.[276]
Urology – also known as genitourinary surgery, is the branch of medicine that focuses on surgical and medical diseases of the male and female urinary-tract system and the male reproductive organs. Organs under the domain of urology include the kidneys, adrenal glands, ureters, urinary bladder, urethra, and the male reproductive organs (testes, epididymis, vas deferens, seminal vesicles, prostate, and penis).
Uterus – The uterus or womb is a major female hormone-responsive secondary sex organ of the reproductive system in humans and most other mammals. In the human, the lower end of the uterus, the cervix, opens into the vagina, while the upper end, the fundus, is connected to the fallopian tubes. It is within the uterus that the fetus develops during gestation. In the human embryo, the uterus develops from the paramesonephric ducts which fuse into the single organ known as a simplex uterus. The uterus has different forms in many other animals and in some it exists as two separate uteri known as a duplex uterus.
V
Vaccine – is a biological preparation that provides active acquired immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. The agent stimulates the body's immune system to recognize the agent as a threat, destroy it, and to further recognize and destroy any of the microorganisms associated with that agent that it may encounter in the future. Vaccines can be prophylactic (to prevent or ameliorate the effects of a future infection by a natural or "wild" pathogen), or therapeutic (e.g., vaccines against cancer, which are being investigated).[277][278][279][280]
Vagina – In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vulva to the cervix. The outer vaginal opening is normally partly covered by a membrane called the hymen. At the deep end, the cervix (neck of the uterus) bulges into the vagina. The vagina allows for sexual intercourse and birth. It also channels menstrual flow (menses), which occurs in humans and closely related primates as part of the monthly menstrual cycle.
Vas deferens – also called ductus deferens, is part of the male reproductive system of many vertebrates; these ducts transport sperm from the epididymis to the ejaculatory ducts in anticipation of ejaculation. It is a partially coiled tube which exits the abdominal cavity through the inguinal canal.
Vastus intermedius muscle – arises from the front and lateral surfaces of the body of the femur in its upper two-thirds, sitting under the rectus femoris muscle and from the lower part of the lateral intermuscular septum. Its fibers end in a superficial aponeurosis, which forms the deep part of the quadriceps femoris tendon.
Vastus lateralis muscle –
Vastus medialis –
Vein –
Vena cava, inferior –
Vena cava, superior –
Ventricle –
Ventricle system –
Venule –
Vertebral column –
Virology – is the study of viral – submicroscopic, parasitic particles of genetic material contained in a protein coat[281][282] – and virus-like agents. It focuses on the following aspects of viruses: their structure, classification and evolution, their ways to infect and exploit host cells for reproduction, their interaction with host organism physiology and immunity, the diseases they cause, the techniques to isolate and culture them, and their use in research and therapy. Virology is considered to be a subfield of microbiology or of medicine.
Visual acuity – (VA), commonly refers to the clarity of vision, but technically rates an examinee's ability to recognize small details with precision. Visual acuity is dependent on optical and neural factors, i.e., (1) the sharpness of the retinal image within the eye, (2) the health and functioning of the retina, and (3) the sensitivity of the interpretative faculty of the brain.[283]
Visual cortex – The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and then reaches the visual cortex. The area of the visual cortex that receives the sensory input from the lateral geniculate nucleus is the primary visual cortex, also known as visual area 1 (V1), Brodmann area 17, or the striate cortex. The extrastriate areas consist of visual areas 2, 3, 4, and 5 (also known as V2, V3, V4, and V5, or Brodmann area 18 and all Brodmann area 19).[284]
Visual field test –
Visual perception –
Vital signs –
Vitamin D –
Vitrectomy –
Vitreous body –
Vulva –
W
Waist – is the part of the abdomen between the rib cage and hips. On people with slim bodies, the waist is the narrowest part of the torso. The waistline refers to the horizontal line where the waist is narrowest, or to the general appearance of the waist.
Wart – Warts are typically small, rough, hard growths that are similar in color to the rest of the skin.[285][286] They typically do not result in other symptoms, except when on the bottom of the feet, where they may be painful.[286] While they usually occur on the hands and feet, they can also affect other locations.[287] One or many warts may appear.[286] They are not cancerous.[286]
Weber test – is a screening test for hearing performed with a tuning fork.[288][289] It can detect unilateral (one-sided) conductive hearing loss (middle ear hearing loss) and unilateral sensorineural hearing loss (inner ear hearing loss). The test is named after Ernst Heinrich Weber (1795–1878). Conductive hearing ability is mediated by the middle ear composed of the ossicles: the malleus, the incus, and the stapes. Sensorineural hearing ability is mediated by the inner ear composed of the cochlea with its internal basilar membrane and attached cochlear nerve (cranial nerve VIII). The outer ear consisting of the pinna, ear canal, and ear drum or tympanic membrane transmits sounds to the middle ear but does not contribute to the conduction or sensorineural hearing ability save for hearing transmissions limited by cerumen impaction (wax collection in the ear canal). The Weber test has had its value as a screening test questioned in the literature.[290][291]
Wernicke–Korsakoff syndrome – (WKS) is the combined presence of Wernicke encephalopathy (WE) and alcoholic Korsakoff syndrome. Due to the close relationship between these two disorders, people with either are usually diagnosed with WKS as a single syndrome. It mainly causes vision changes, ataxia and impaired memory.[292]
Wernicke's area – also called Wernicke's speech area, is one of the two parts of the cerebral cortex that are linked to speech, the other being Broca's area. It is involved in the comprehension of written and spoken language, in contrast to Broca's area, which is involved in the production of language. It is traditionally thought to reside in Brodmann area 22, which is located in the superior temporal gyrus in the dominant cerebral hemisphere, which is the left hemisphere in about 95% of right-handed individuals and 60% of left-handed individuals.
Whiplash – is a non-medical term describing a range of injuries to the neck caused by or related to a sudden distortion of the neck[293] associated with extension,[294] although the exact injury mechanisms remain unknown. The term "whiplash" is a colloquialism. "Cervical acceleration–deceleration" (CAD) describes the mechanism of the injury, while the term "whiplash associated disorders" (WAD) describes the injury sequelae and symptoms.
White blood cell – White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from multipotent cells in the bone marrow known as hematopoietic stem cells. Leukocytes are found throughout the body, including the blood and lymphatic system.[295]
White matter – refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts.[296] Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distribution of action potentials, acting as a relay and coordinating communication between different brain regions.[297]
Working memory – is a cognitive system with a limited capacity that can hold information temporarily.[298] Working memory is important for reasoning and the guidance of decision-making and behavior.[299][300] Working memory is often used synonymously with short-term memory, but some theorists consider the two forms of memory distinct, assuming that working memory allows for the manipulation of stored information, whereas short-term memory only refers to the short-term storage of information.[299][301] Working memory is a theoretical concept central to cognitive psychology, neuropsychology, and neuroscience.
Wrist – In human anatomy, the wrist is variously defined as 1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand;[302][303] (2) the wrist joint or radiocarpal joint, the joint between the radius and the carpus [303] and; (3) the anatomical region surrounding the carpus including the distal parts of the bones of the forearm and the proximal parts of the metacarpus or five metacarpal bones and the series of joints between these bones, thus referred to as wrist joints.[304][305] This region also includes the carpal tunnel, the anatomical snuff box, bracelet lines, the flexor retinaculum, and the extensor retinaculum. As a consequence of these various definitions, fractures to the carpal bones are referred to as carpal fractures, while fractures such as distal radius fracture are often considered fractures to the wrist.
X
Xanthoma – A xanthoma (pl. xanthomas or xanthomata) (condition: xanthomatosis), from Greek ξανθός (xanthós) 'yellow', is a deposition of yellowish cholesterol-rich material that can appear anywhere in the body in various disease states.[306] They are cutaneous manifestations of lipidosis in which lipids accumulate in large foam cells within the skin.[306] They are associated with hyperlipidemias, both primary and secondary types.
Y
Yaws – is a tropical infection of the skin, bones and joints caused by the spirochete bacterium Treponema pallidum pertenue.[307][308] The disease begins with a round, hard swelling of the skin, 2 to 5 centimeters in diameter.[307] The center may break open and form an ulcer.[307] This initial skin lesion typically heals after three to six months.[309] After weeks to years, joints and bones may become painful, fatigue may develop, and new skin lesions may appear.[307] The skin of the palms of the hands and the soles of the feet may become thick and break open.[310] The bones (especially those of the nose) may become misshapen.[311] After five years or more large areas of skin may die, leaving a scar.[307]
Yellow fever – is a viral disease of typically short duration.[312] In most cases, symptoms include fever, chills, loss of appetite, nausea, muscle pains particularly in the back, and headaches.[313] Symptoms typically improve within five days.[314] In about 15% of people, within a day of improving the fever comes back, abdominal pain occurs, and liver damage begins causing yellow skin.[315][316] If this occurs, the risk of bleeding and kidney problems is increased.[317]
Z
Zellweger spectrum disorders – are a group of rare disorders that create the same disease process.[318] The subdivisions of this spectrum are hyperpipecolic acidemia, Infantile Refsum disease, neonatal adrenoleukodystrophy (NALD), and Zellweger syndrome. It can also be referred to as Peroxisomal Biogenesis Disorders, Zellweger Syndrome Spectrum, NALD, Cerebrohepatorenal Syndrome, and ZSS.[319] It can affect many body organs, including the kidneys, eyes, and hearing.[320] It is named after Hans Zellweger.
Zika virus – (ZIKV) (pronounced /ˈziːkə/ or /ˈzɪkə/[321][322]) is a member of the virus family Flaviviridae.[323] It is spread by daytime-active Aedes mosquitoes, such as A. aegypti and A. albopictus.[323] Its name comes from the Ziika Forest of Uganda, where the virus was first isolated in 1947.[324] Zika virus shares a genus with the dengue, yellow fever, Japanese encephalitis, and West Nile viruses.[324] Since the 1950s, it has been known to occur within a narrow equatorial belt from Africa to Asia. From 2007 to 2016, the virus spread eastward, across the Pacific Ocean to the Americas, leading to the 2015–2016 Zika virus epidemic.[325]
Zoonosis – A zoonosis (plural zoonoses, or zoonotic diseases) is an infectious disease caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) that has jumped from a non-human animal (usually a vertebrate) to a human.[326][327][328] Typically, the first infected human transmits the infectious agent to at least one other human, who, in turn, infects others.
Zygomatic bone – In the human skull, the zygomatic bone (cheekbone or malar bone) is a paired irregular bone which articulates with the maxilla, the temporal bone, the sphenoid bone and the frontal bone. It is situated at the upper and lateral part of the face and forms the prominence of the cheek, part of the lateral wall and floor of the orbit, and parts of the temporal fossa and the infratemporal fossa. It presents a malar and a temporal surface; four processes (the frontosphenoidal, orbital, maxillary, and temporal), and four borders.
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