Glossary of Astronomy, Business, Elec, Nano, Psychiatry, Robotics,

 

 

 A
A-type star
absolute magnitude
    A measure of a star's absolute brightness. It is defined as the apparent magnitude the star would show if it were located at a distance of 10 parsecs, or 32.6 light-years.
accretion disk
    A roughly circular mass of diffuse material in orbit around a central object, such as a star or black hole. The material is acquired from a source external to the central object, and friction causes it to spiral inward towards the object.
active galactic nucleus (AGN)
    A compact region in the center of a galaxy displaying a much higher than normal luminosity over some part of the electromagnetic spectrum with characteristics indicating that the luminosity is not produced by stars. A galaxy hosting an AGN is called an active galaxy.
albedo
    A measure of the proportion of the total solar radiation received by an astronomical body, such as a planet, that is diffusely reflected away from the body. It is a dimensionless quantity typically measured on a scale from 0 (indicating total absorption of all incident radiation, as by a black body) to 1 (indicating total reflection). The albedo reported for an astronomical body may vary widely by the spectral and angular distribution of the incident radiation, by the "layer" of the body being measured (e.g. upper atmosphere versus surface), and by local variation within these layers (e.g. cloud cover and geological or environmental surface features).

Syrtis Major (center) is a prominent dark albedo feature on Mars
albedo feature
    A large area on the surface of a reflecting object that shows a significant contrast in brightness or darkness (albedo) compared to adjacent areas.
Am star
    A chemically peculiar star belonging to the more general class of A-type stars. The spectrum of the Am stars shows abnormal enhancements and deficiencies of certain metals. See metallicity.
aphelion
    The point at which a body orbiting the Earth's Sun is furthest from the Sun. Contrast perihelion.
apoapsis
    The point at which an orbiting body is furthest from its primary. Contrast periapsis.
apogee
    The point at which a body orbiting the Earth (such as the Moon or an artificial satellite) is furthest from the Earth. Contrast perigee.
apparent magnitude

Also called visual brightness (V).
    A measure of the brightness of a celestial body as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere. The brighter the object appears, the lower its magnitude.
appulse
    The closest approach of one celestial object to another, as viewed from a third body.
apsis
    In the orbit of a planetary body, one of the two extreme points of distance between the body and its primary – either the point of minimal distance, called the periapsis, or the point of maximal distance, called the apoapsis. The term may also be used to refer to the value of the distance rather than the point itself. All elliptical orbits have exactly two apsides.
argument of periapsis

Also called the argument of perifocus or argument of pericenter.
    The angle from an orbiting body's ascending node to its periapsis, measured in the direction of motion. It is one of six canonical orbital elements used to characterize an orbit.
artificial satellite
    An object that has been intentionally placed into orbit by humans, often around the Earth but also around other bodies within the Solar System. Contrast natural satellite.
ascending node

Also called the north node.
    The orbital node at which an orbiting object moves north through the plane of reference (in geocentric and heliocentric orbits) or at which the orbiting object moves away from the observer (in orbits outside of the Solar System). The position of the ascending node with respect to a reference direction, called the longitude of the ascending node, is used along with other parameters to describe an orbit. Contrast descending node.
asterism
    Any pattern of stars recognizable in Earth's night sky. An asterism may form part of an official constellation or it may be composed of stars from more than one constellation.
asteroid
asteroid belt
    The circumstellar disc in the Solar System located roughly between the orbits of Mars and Jupiter that is occupied by numerous irregularly shaped small Solar System bodies ranging in size from dust particles to asteroids and minor planets. The asteroid belt is often called the main asteroid belt or main belt to distinguish it from other asteroid populations in other parts of the Solar System.
astrobiology
astrodynamics
    See orbital mechanics.
astrogeology
astrometric binary
    A type of binary system where evidence for an unseen orbiting companion is revealed by its periodic gravitational perturbation of the visible component. See also spectroscopic binary.
astrometry
    The branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies.
astronomical body

Also called a celestial body.
    A type of naturally occurring physical entity, association, or structure within the observable universe that is a single, tightly bound, contiguous structure, such as a star, planet, moon, or asteroid. Though the terms astronomical "body" and astronomical "object" are often used interchangeably, there are technical distinctions.
astronomical catalogue

Also spelled astronomical catalog.
astronomical object

Also called a celestial object.
    A type of naturally occurring physical entity, association, or structure that exists within the observable universe but is a more complex, less cohesively bound structure than an astronomical body, consisting perhaps of multiple bodies or even other objects with substructures, such as a planetary system, star cluster, nebula, or galaxy. Though the terms astronomical "object" and astronomical "body" are often used interchangeably, there are technical distinctions.
astronomical symbol
astronomical unit (AU)
    A unit of length used primarily for measuring astronomical distances within the Solar System or between the Earth and distant stars. Originally conceived as the approximate average distance between the centers of the Earth and the Sun, the astronomical unit is now more rigidly defined as exactly 149,597,870.7 kilometres (92,956,000 miles; 4.8481×10−6 parsecs; 1.5813×10−5 light-years).
astronomy
    The scientific study of celestial objects and phenomena, the origins of those objects and phenomena, and their evolution.
astrophotography
astrophysics
    The branch of astronomy that employs principles of physics and chemistry to determine the nature of astronomical objects and phenomena, examining properties such as luminosity, density, temperature, and chemical composition (rather than the positions or motions of objects in space, which is more specifically the emphasis of celestial mechanics).
atmosphere
axial precession
    A slow, continuous, gravity-induced change (a precession) in the orientation of an astronomical body's axis of rotation. The term often refers in particular to the gradual shift in the orientation of Earth's rotational axis with respect to its orbital plane over a cycle of approximately 25,772 years, which is caused predominantly by the gravitational influence of the Moon and the Sun on the Earth's equatorial bulge. The phenomenon is similar to but much larger in magnitude than other changes in the alignment of Earth's axis such as nutation and polar motion, and is the cause of the apparent precession of the equinoxes in the night sky.
axial tilt

Also called obliquity.
    The angle between an object's rotational axis and its orbital axis, or, equivalently, the angle between its equatorial plane and orbital plane. Axial tilt usually does not change considerably during a single orbital period; Earth's axial tilt is the cause of the seasons. Axial tilt is distinct from orbital inclination.
axis of rotation
azimuth
    An angular measurement of an object's orientation along the horizon of the observer, relative to the direction of true north. When combined with the altitude above the horizon, it defines an object's current position in the spherical coordinate system.

B
barycenter
    The common center of mass about which any two or more bodies of a gravitationally bound system orbit. The barycenter is one of the foci of the elliptical orbit of each body participating in the system; its location is strongly influenced by the mass of each body and the distances between them. For example, in a planetary system where the mass of the central star is significantly larger than the mass of an orbiting planet, the barycenter may actually be located within the radius of the star, such that the planet appears to orbit the star itself, though both bodies actually orbit the shared barycenter.

Two bodies of similar mass orbiting a common barycenter that is external to both bodies (a common situation for binary star systems)
baryogenesis
    The process by which the class of subatomic particles known as baryons were generated in the early Universe, including the means by which baryons outnumber antibaryons.
Big Bang
    The prevailing cosmological model for the origin of the observable universe. It depicts a starting condition of extremely high density and temperature, followed by an ongoing expansion that led to the current conditions.
binary star
    A star system consisting of exactly two stars orbiting around their common barycenter. The term is often used interchangeably with double star, though the latter can also refer to an optical double star, a type of optical illusion which is entirely distinct from true binary star systems.
black hole
    A concentration of mass so compact that it creates a region of space from which not even light can escape. The outer boundary of this region is called the event horizon.
blazar
break-up velocity

Also called critical velocity or critical rotation.
    The surface velocity at which the centrifugal force generated by a rapidly spinning star matches the force of Newtonian gravity. At rotational velocities beyond this point, the star begins to eject matter from its surface.[1]
brown dwarf
    A substellar object that is too low in mass to sustain the nuclear fusion of hydrogen-1 in its core, with the latter being a characteristic of stars on the main sequence. Brown dwarfs can still generate energy from gravitational contraction and by the fusion of deuterium.
bulge

C

celestial equator
    The imaginary great circle of a body's celestial sphere that is coplanar with the body's terrestrial equator. On Earth, the plane of the celestial equator is the basis of the equatorial coordinate system. Due to Earth's axial tilt, the celestial equator is currently inclined at an angle of 23.44 degrees with respect to the ecliptic.
celestial mechanics
    The branch of astronomy that studies the motions of all types of astronomical objects, including stars, planets, and natural and artificial satellites, among others.
celestial pole
    One of two coordinates in the Earth's sky at which a hypothetical indefinite extension of the Earth's axis of rotation "intersects" the celestial sphere. The celestial poles form the north and south poles of the equatorial coordinate system.
celestial sphere
    An imaginary sphere that covers the Earth's entire sky and is stationary with respect to the background stars. It is used as a tool for spherical astronomy.
centaur
central massive object (CMO)
    Any very large concentration of mass at the center of a galaxy, typically either a supermassive black hole or a compact stellar nucleus, but sometimes both.
chromosphere
chromospheric activity index
    A parameter indicating the magnetic activity in a star's chromosphere. One measure of this activity is log R′HK, where R′HK is the ratio of the equivalent width of a star's singly ionized calcium H and K lines, after correction for photospheric light, to the bolometric flux.[2] Schröder et al. (2009) divide solar-type stars into four groups depending on their activity index: very active (log R′HK above −4.2), active (−4.2 to −4.75), inactive (−4.75 to −5.1), and very inactive (below −5.1).[3]
circumstellar disc

Also spelled circumstellar disk.
cis-Neptunian object (CNO)
clearing the neighbourhood
color index
    A numeric value that is used to compare the brightness of a star measured from different frequency bands of the electromagnetic spectrum. Because the energy output of a star varies by frequency as a function of temperature, the color index can be used to indicate the star's temperature.
comet
    A relatively small, icy body that displays extended features when it approaches the Sun. The energy from the Sun vaporizes volatiles on a comet's surface, producing a visible coma around the cometary body. Sometimes a comet can produce a long tail radiating away from the Sun.
commensurability
    A property of two objects orbiting the same body whose orbital periods are in a rational proportion. For example, the orbital period of Saturn around the Sun is very nearly 5/2 the orbital period of Jupiter.
common proper motion
    A term used to indicate that two or more stars share the same motion through space, within the margin of observational error. That is, either they have nearly the same proper motion and radial velocity parameters, which may suggest that they are gravitationally bound or share a common origin,[4] or they are known to be gravitationally bound (in which case their proper motions may be rather different but average to be the same over time).
compact star

Also called a compact object.
    Any astronomical body with a very high mass relative to its radius, compared to most ordinary atomic matter, typically very high-density objects such as white dwarfs, neutron stars, and black holes, or to stellar remnants with very small radii compared to ordinary stars.
compact stellar nucleus
    See nuclear star cluster.
conjunction
    A phenomenon during which two astronomical objects or spacecraft have either the same right ascension or the same ecliptic longitude as observed from a third body (usually the Earth), such that, from the observer's perspective, the objects appear to closely approach each other in the sky.
constellation
    A region on the celestial sphere surrounding a specific and identifiable grouping of stars. The names of constellations are assigned by tradition and often have an associated folklore based in mythology, while the modern demarcation of their borders was established by the International Astronomical Union in 1930. Compare asterism.
corona
    An aura of plasma that surrounds cooler stars such as the Sun. It can be observed during a solar eclipse as a bright glow surrounding the lunar disk. The temperature of the corona is much higher than that of the stellar surface, and the mechanism that creates this heat remains subject to debate among astronomers.
coronal mass ejection (CME)
    A significant release of plasma and the accompanying magnetic field from the Sun's corona, often following a solar flare or present during a solar prominence eruption.
cosmic distance ladder
cosmic dust

Also called space dust.
    Dust which exists in outer space or has fallen on Earth, generally composed of fine particles of solid matter far smaller than those found in terrestrial dust.
cosmic microwave background (CMB)

Also called the cosmic microwave background radiation (CMBR).
cosmic ray
    A type of radiation consisting of high-energy protons and atomic nuclei which move through space at nearly the speed of light, and which may originate from the Sun or from outside the Solar System. Collisions of cosmic rays with the Earth's atmosphere can produce dramatic effects both in the air and on the surface.
cosmogony
    Any model concerning the origin of either the universe or the cosmos.
cosmology
    The scientific study of the origin, evolution, and eventual fate of the Universe.
critical rotation
critical velocity

Also called break-up velocity.
    The surface velocity at the equator of a rotating body where the centrifugal force balances the Newtonian gravity. At this rotation rate, mass can be readily lost from the equator, forming a circumstellar disc. See also break-up velocity.[5]
culmination

D
debris disk
    A ring-shaped circumstellar disc of dust and debris orbiting its host star. It is created by collisions between planetesimals. A debris disk can be discerned from an infrared excess being emitted from the star system, as the orbiting debris re-radiates the star's energy into space as heat.

Circumstellar debris disks as detected by the Hubble Space Telescope, and artist's impressions of the disks' orientations around their host stars
declination
    In the equatorial coordinate system, the celestial equivalent of terrestrial latitude. Coordinates north of the celestial equator are measured in positive degrees from 0° to 90°, while coordinates to the south use coordinates in negative degrees. See also right ascension.
decretion disk
    A circumstellar disc formed from gas ejected from a central star that now follows a nearly Keplerian orbit around it. This type of disk can be found around many Be stars.[6]
deep-sky object (DSO)
    Any astronomical object that is not an individual star or an object within the Earth's Solar System. The classification is used mostly in amateur observational astronomy to distinguish faint objects in the night sky such as star clusters, nebulae, and galaxies.
descending node

Also called the south node.
    The orbital node at which an orbiting object moves south through the plane of reference (in geocentric and heliocentric orbits) or at which the orbiting object moves toward the observer (in orbits outside of the Solar System). Contrast ascending node.
detached object
direct motion
    See prograde motion.
diurnal motion
    The apparent motion of an astronomical object (e.g. the Sun, a planet, or a distant star) around the two celestial poles in the Earth's night sky over the course of one day. Diurnal motion is caused by Earth's rotation about its own axis, such that every object appears to follow a circular path called the diurnal circle.
double star
    Any pair of stars which appear near each other on the celestial sphere, either because the two stars coincidentally lie along nearly the same line of sight from the Earth despite being physically distant from each other, or because the two stars are actually located in physical proximity to each other, by which they may form a co-moving pair or a binary star system.
dwarf planet
dwarf star
    The category of ordinary main sequence stars like the Sun, in contrast to evolved giant stars like Betelgeuse and Antares. Confusingly, the term has also come to include stellar remnants known as white dwarfs as well as low-mass substellar objects known as brown dwarfs.

E
early-type star
    A hotter and more massive star, in contrast to late-type stars that are cooler and less massive. The term originated from historical stellar models that assumed stars began their early life at a high temperature then gradually cooled off as they aged. It may be used to refer to the higher-temperature members of any particular population or category of stars, rather than of all stars in general.
eccentricity
    See orbital eccentricity.
ecliptic coordinate system
ecliptic plane

Also called the plane of the ecliptic or simply the ecliptic.
    The plane defined by the Earth's orbit around the Sun. Hence, the position of the Sun as viewed from the Earth defines the intersection of this plane with the celestial sphere. The ecliptic is widely used as a reference plane for describing the position of other Solar System bodies within various celestial coordinate systems. It differs from the celestial equator because of the axial tilt of the Earth.
effective temperature
    (of a star or planet) The temperature of an ideal black body that would emit the same total amount of electromagnetic radiation.
elliptical galaxy
    A type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless appearance. They are one of three main morphological classes of galaxy, along with spiral and lenticular galaxies.
elliptical orbit

Also elliptic orbit.
    A type of Kepler orbit with an orbital eccentricity of less than 1 (often inclusive of circular orbits, which have eccentricity equal to 0), or one with negative energy. Elliptical orbits take the shape of an ellipse, and are very common in two-body astronomical systems.
A relatively small body (such as a planet) orbiting a larger one (such as a star) in an elliptical orbit, with the larger body located at one of the focal points of the ellipse
elongation
    The angular separation between the Sun and an orbiting body, such as a planet, as it appears from Earth.
ephemeris
    A list or table of the expected positions of astronomical objects or artificial satellites in the sky at various dates and times. Modern ephemerides are often provided by computer software.
epoch
    A moment in time used as a reference point for some time-varying astronomical quantity, such as the celestial coordinates or orbital elements of an astronomical object, because such quantities are subject to perturbations and change over time. The primary use of astronomical quantities specified by epochs is to calculate other relevant parameters of motion in order to predict future positions and velocities. In modern usage, astronomical quantities are often specified as a polynomial function of a particular time interval, with a given epoch as the temporal point of origin.
equator
    The imaginary line on a gravitationally rounded spheroid such as a planet that represents the intersection of the spheroid's surface with a plane perpendicular to its axis of rotation and equidistant from its geographical poles. The plane of the Earth's terrestrial equator is the basis for the celestial equator.
equatorial coordinate system
equinox
    One of two precise times of year when the imaginary plane of the Earth's equator, extended indefinitely in all directions, passes through the center of the Sun, or, equivalently, when the Sun's apparent geocentric longitude is either 0 degrees or 180 degrees.[7] The equinoxes occur on or near March 20 and September 22 each year. On the day of an equinox, the center of the visible Sun appears to be directly above the equator, and the durations of day and night are approximately equal all over the planet. Contrast solstice.
escape velocity
    The minimum speed that must be achieved for a free, non-propelled object to escape from the gravitational influence of a massive body, i.e. to achieve an infinite distance from it; more generally, escape velocity is the speed at which the sum of an object's kinetic energy and gravitational potential energy is equal to zero. It is a function of the mass of the body and the object's distance to its center of mass. An object which has achieved escape velocity is neither on the surface nor in a closed orbit of any radius.
evolutionary track
    A curve on the Hertzsprung–Russell diagram that a solitary star of a particular mass and composition is expected to follow during the course of its evolution. This curve predicts the combination of temperature and luminosity that a star will have during part or all of its lifetime.[8]

Sample evolutionary tracks for stars of different mass
extinction
    The absorption and scattering of electromagnetic radiation by matter (dust and gas) between an emitting astronomical object and the observer. Atmospheric extinction varies by the wavelength of the radiation, with the attenuation being greater for blue light than for red.
extragalactic astronomy
    The branch of astronomy that studies objects and phenomena outside of the Milky Way galaxy, i.e. all objects not covered by galactic astronomy.
extrasolar object
    Any astronomical object that exists outside the Solar System. The term is generally not applied to stars or any objects larger than a star or the Solar System itself, such as galaxies.
extrasolar planet

Also called an exoplanet.
    Any planet outside the Earth's Solar System.

F

facula
    A bright spot on a star's photosphere formed by concentrations of magnetic field lines. For the Sun in particular, faculae are most readily observed near the solar limb. An increase in faculae as a result of a stellar cycle increases the star's total irradiance.
field galaxy
    Any galaxy that does not belong to a larger cluster of galaxies and is gravitationally isolated.
field star
    A randomly situated star that lies along the line of sight to a group of physically associated stars under study, such as a star cluster. These field stars are important to identify in order to prevent them from contaminating the results of a study.[9]
first light
    The first use of a newly constructed telescope or other instrument to take an astronomical image.
First Point of Aries (♈︎)

Also called the Cusp of Aries.
    The location of the March equinox upon the celestial sphere, used as a reference point in celestial coordinate systems. Located in the constellation Pisces, the First Point of Aries defines the ecliptic coordinate of (0°, 0°) and represents the point at which the Sun meets the celestial equator while traveling from south to north each year. It is directly opposite the First Point of Libra.
First Point of Libra
    The location of the September equinox upon the celestial sphere, used as a reference point in celestial coordinate systems. Located in the constellation Virgo, the First Point of Libra represents the point at which the Sun meets the celestial equator while traveling from north to south each year. It is directly opposite the First Point of Aries.
fixed stars

Also called background stars.
    The "background" of astronomical objects in the night sky which are so distant from observers on Earth that they do not appear to move relative to each other, as opposed to the "foreground" of objects within the Solar System which do. The fixed stars are typically taken to include all stars other than the Sun, as well as all other extrasolar and deep-sky objects.
flare star
    A class of variable star that undergoes sudden, dramatic increases in brightness due to magnetic activity on its surface. This change in brightness occurs across the electromagnetic spectrum from radio waves to X-rays. Most flare stars are faint red dwarfs.
Fulton gap
    The apparent uncommonness of planets having a size between 1.5 and 2 times that of the Earth.

G
galactic astronomy
    The branch of astronomy that studies objects and phenomena within the Milky Way galaxy, as opposed to everything outside of the Milky Way, which is the domain of extragalactic astronomy.
galactic anticenter
Galactic Center
    The rotational center of the Milky Way galaxy, consisting of a supermassive black hole of 4.100 ± 0.034 million solar masses. It is approximately 8,200 parsecs (27,000 ly) away from Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius, where the Milky Way appears brightest.
galactic coordinate system
galactic corona
galactic nucleus

Also called the galactic core or galactic center.
    The region at the center of a galaxy, usually home to a very dense concentration of stars and gas. It almost always includes a supermassive black hole which, when active, can generate a much higher luminosity in a compact region than its surroundings. This excess luminosity is known as an active galactic nucleus, and the brightest such active galaxies are known as quasars.
galactic period

Also called the galactic year or cosmic year.
    The time a given astronomical object within a galaxy takes to complete one orbit around the galactic center. Estimates of the duration of one revolution of the Solar System about the center of the Milky Way range from 225 to 250 million terrestrial years.
galactic tide
    The tidal force experienced by objects subject to the gravitational field of a galaxy such as the Milky Way.
galaxy
    A large, gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter, each of which orbits a center of mass. Galaxies may contain hundreds of billions of stars and are categorized according to their visual morphology as elliptical, spiral, or irregular. Most of the galaxies in the observable universe are between 1,000 and 3,000 parsecs (3,300 and 9,800 ly) in diameter though some, including the Milky Way, are much larger.
galaxy cluster
    A large-scale structure consisting of hundreds or thousands of galaxies bound together by gravity. Galaxy clusters are distinct from similarly named galactic clusters and other types of star clusters and from smaller aggregates of galaxies known as galaxy groups. Galaxy groups and galaxy clusters can themselves cluster together to form superclusters.
galaxy group
Galilean moons
    A collective name for the four moons of Jupiter discovered by Galileo Galilei in 1610: Io, Europa, Ganymede, and Callisto.
gamma-ray astronomy
    The subfield of astronomy that studies astronomical objects detectable at gamma-ray wavelengths.
gamma-ray burst (GRB)
    A cataclysmic event that generates a brief but intense outburst of gamma ray radiation which can be detected from billions of light-years away. The source of most GRBs is theorized to be supernova or hypernova explosions of high-mass stars. Short GRBs may also result from the collision of neutron stars.
gas giant
    A giant planet composed mainly of hydrogen and helium gases rather than heavier elements, e.g. Jupiter and Saturn in the Solar System.
geocentric
    Centered upon the Earth, e.g. a geocentric orbit.
geometric albedo
    The ratio of the brightness of an astronomical body at a phase angle of zero to an idealized flat, fully reflecting, diffusively scattering (Lambertian) disk with the same cross-section. It is a measure of how much of the incoming illumination is being scattered back toward an observer and has a value between zero and one.
geostationary orbit

Also called a geosynchronous equatorial orbit (GEO).
    A circular geosynchronous orbit, which maintains a constant altitude of 35,786 kilometres (22,236 mi) directly above Earth's equator in the same direction as Earth's rotation such that, to an observer on Earth's surface, the orbiting object appears motionless, in a fixed position in the sky. Artificial satellites are often placed in geostationary orbit so that antennas on Earth do not have to rotate to track them.
geosynchronous orbit (GSO)
    A synchronous orbit about the Earth, i.e. with an orbital period equal to Earth's rotational period, such that the orbiting object appears to return to exactly the same position in the sky after a period of one sidereal day. All geosynchronous orbits have a semi-major axis equal to 35,786 kilometres (22,236 mi); geostationary orbits are a special case of geosynchronous orbits.
giant planet
    Any very large or massive planet, including gas giants and ice giants.
globular cluster
    A tight, spherical conglomeration of many thousands of stars which are gravitationally bound to each other and which orbit a galactic core as a satellite. They differ from open clusters in having a much higher combined mass, with a typical lifespan extending for billions of years.
gravitational collapse
gravitational lens
    Any very large distribution of mass, such as a galactic cluster, which can bend passing light from a distant source by a noticeable degree. The effect, known as gravitational lensing, can make background objects appear to an observer to take on a ring or arc shape.

A luminous red galaxy (LRG) acting as a gravitational lens, distorting the light from a much more distant blue galaxy into an Einstein ring
gravitational-wave astronomy
    A branch of observational astronomy which analyzes minute distortions in the curvature of spacetime known as gravitational waves to collect observational data about astronomical objects and events such as neutron stars, black holes, supernovae, and the Big Bang.

H

H II region
    An ionized nebula powered by young, massive O-type stars. Ultraviolet photons from these hot stars ionize gas in the surrounding environment, and the nebular gas shines brightly in spectral lines of hydrogen and other elements. Because O-type stars have relatively short lifetimes (typically a few million years), the presence of an H II region indicates that massive star formation has taken place recently at that location. H II regions are often found in the arms of spiral galaxies and in star-forming irregular galaxies.
heliocentric
    Centered upon the Earth's Sun, e.g. a heliocentric orbit.
heliopause
heliosphere
    The vast, bubble-like cavity in the interstellar medium which surrounds and is created by the plasma emanating from the Earth's Sun. The heliosphere encompasses the entirety of the Solar System and a vast region of space beyond it. Its outer limit is often considered the boundary between matter originating from the Sun and matter originating from the rest of the galaxy.
Hertzsprung–Russell diagram
    A plot of luminosity versus effective temperature for a population of stars; depending on the usage, the star's absolute magnitude may be substituted for luminosity, and its color index or spectral type for temperature. Single stars of known mass and composition follow predictable tracks across this chart over the course of their evolution. Hence, knowing a star's mass and metallicity allows its age to be estimated. Stars of similar types are also found grouped together in specific regions of the chart, including main sequence, red giant, and white dwarf stars.
Hill sphere

Also called the Hill radius.
    The approximate region around an astronomical object within which its gravitational attraction dominates the motions of satellites. It is computed with respect to the next most gravitationally attractive object, such as the nearest star or the galactic core. Satellites moving outside this radius tend to be perturbed away from the main body.[10]
hypergalaxy
    A system consisting of a large galaxy accompanied by multiple smaller satellite galaxies (often elliptical) as well as its galactic corona. The Milky Way and Andromeda systems are examples of hypergalaxies.[11]

I

ice giant
    A giant planet composed mainly of elements heavier than hydrogen or helium (such as oxygen, carbon, nitrogen, and sulfur), especially chemical volatiles with freezing points above 100 K (−173 °C), e.g. Uranus and Neptune in the Solar System.
inclination
    See orbital inclination.
inferior planet
    An archaic term that is sometimes used to refer to the planets Mercury and Venus. The name originated from the fact that these planets orbit closer to the Sun than the Earth and hence, in the geocentric cosmology of Ptolemy, both appeared to travel with the Sun across the sky. This is in contrast to the so-called superior planets, such as Mars, which appeared to move independently of the Sun.
infrared astronomy
    The subfield of astronomy that studies astronomical objects detectable at infrared wavelengths.
International Astronomical Union (IAU)
interstellar medium (ISM)
    The matter that exists in the space between the stars in a galaxy. This medium mainly consists of hydrogen and helium, but is enhanced by traces of other elements contributed by matter expelled from stars.
interstellar reddening
    An effect produced by the incremental absorption and scattering of electromagnetic energy from interstellar matter, known as extinction. This effect causes the more distant objects such as stars to appear redder and dimmer than expected. It is not to be confused with the separate phenomenon of redshift.
invariable plane

Also called Laplace's invariable plane or the Laplace plane.
    The imaginary plane passing through the barycenter of a planetary system and perpendicular to its angular momentum vector, and which may be regarded as the weighted average of all planetary orbital and rotational planes comprising the system.
ionosphere
irregular galaxy
irregular moon
    A natural satellite following a distant, inclined, and often eccentric and retrograde orbit about its primary. Irregular moons are thought to be captured from other orbits, as opposed to regular moons, which are thought to form in situ.
isochrone
    A curve on the Hertzsprung–Russell diagram that represents the evolutionary positions of stars having the same age but differing masses. This is in contrast to an evolutionary track, which is a plot of stars having the same mass but differing ages. In fact, multiple evolutionary tracks can be used to build isochrones by putting curves through equal-age points along the tracks. When the mass of a star can be determined, an isochrone can be used to estimate the star's age.

J

Jeans instability
    A physical state in which an interstellar cloud of gas will begin to undergo collapse and form stars. A cloud can become unstable against collapse when it cools sufficiently or has perturbations of density, allowing gravity to overcome the gas pressure.
Julian year (a)
    A unit of time defined as exactly 365.25 days of 86,400 SI seconds each. Because these are units of constant duration, the Julian year is also constant and does not vary with a specific calendar or with any of the other means of determining the length of a year, such as the tropical year. It is therefore widely used as the basis for defining the standard astronomical epoch and the light-year.

K

Kelvin–Helmholtz mechanism
Kepler orbit

Also called a Keplerian orbit.
    The motion of one orbiting body relative to another, as an ellipse, parabola, or hyperbola, which forms a two-dimensional orbital plane (or sometimes a straight line) in three-dimensional space. Kepler orbits are idealized mathematical constructions which consider only the point-like gravitational attraction of two bodies, neglecting more complex orbital perturbations that may exist in reality.
Kuiper belt

Also called the Edgeworth–Kuiper belt.
    A circumstellar disc of small Solar System bodies such as asteroids, trojans, and centaurs in the outer Solar System, extending between 30 and 50 AU from the Sun. It is similar to the asteroid belt but far larger, and is home to several dwarf planets, including Pluto.

L

Lagrangian point

Also called a Lagrange point, libration point, or L-point.
    Any of a set of points near two large bodies in orbit at which a smaller object will maintain a constant position relative to the larger bodies. At other locations, a small object would eventually be pulled into its own orbit around one of the large bodies, but at the Lagrangian points the gravitational forces of the large bodies, the centripetal force of orbital motion, and (in certain scenarios) the Coriolis acceleration all align in a way that causes the small object to become "locked" in a stable or nearly stable relative position. For each combination of two orbital bodies, there are five such Lagrangian points, typically identified with the labels L1 to L5. The phenomenon is the basis for the stable orbits of trojan satellites and is commonly exploited by man-made satellites.
Laniakea Supercluster

Also called the Lenakaeia Supercluster, Local Supercluster, or Local SCI.
late-type star
libration
    A slight oscillating motion of the Moon as seen from the Earth, a result of the Moon's elliptical orbit. It can allow normally hidden parts of the Moon's far side to be visible along the limbs of the lunar disk.
light-year (ly)
    A unit of length used to express astronomical distances that is equivalent to the distance that an object moving at the speed of light in a vacuum would travel in one Julian year: approximately 9.46 trillion kilometres (9.46 x 1012 km) or 5.88 trillion miles (5.88 x 1012 mi). Though the light-year is often used to measure galactic-scale distances in non-specialist publications, the unit of length most commonly used in professional astrometry is the parsec.
limb darkening
    An optical effect seen in stars (including the Sun), where the center part of the disk appears brighter than the edge or limb of the image.
line of apsides
    The imaginary line connecting the two apsides (the periapsis and the apoapsis) of an elliptical orbit, and which therefore represents the distance of the orbit's longest axis.
Local Group
longitude of the ascending node (☊ or Ω)
    The angle between a specified reference direction, called the origin of longitude, and the direction of an orbit's ascending node, as measured on a specified plane of reference. The angle is typically measured eastwards from the reference direction to the ascending node (i.e. counterclockwise as seen from the north). It is one of six canonical orbital elements used to characterize an orbit.
luminosity
    The total amount of energy emitted per unit time by a star, galaxy, or other astronomical object. In SI units, luminosity is measured in joules per second or watts, and is often given in terms of astronomical magnitude. Luminosity is related to but distinct from visual brightness.
lunar phases

M

magnetosphere
    A mostly convex region formed when a plasma, such as the solar wind, interacts with the magnetic field of a body, such as a planet or star.
magnitude
    A numerical logarithmic scale indicating the brightness of an astronomical object, where the lower the value, the brighter the object. By convention, a first magnitude star is 100 times as bright as a sixth magnitude star. Magnitude 6 is considered the lower limit of objects that can be seen with the naked eye, although this can vary depending on seeing conditions and eyesight.
main sequence
    A category of stars which form a continuous and distinctive band on plots of stellar temperature versus luminosity. These stars are characterized by being in hydrostatic equilibrium and undergoing nuclear fusion of hydrogen-1 in their core region. The Sun is a main sequence star.
March equinox

Also called the Northward equinox.
    The precise time of year on Earth when the Sun appears to cross the celestial equator, while generally trending northward at each zenith passage. It represents the moment at which the North Pole of the Earth begins to tilt toward the Sun, and typically occurs on or near March 20 each year. It is the vernal equinox in the Northern Hemisphere and the autumnal equinox in the Southern Hemisphere. Contrast September equinox.
mean anomaly (M)
    The fraction of an elliptical orbit's period that has elapsed since the orbiting body passed periapsis, expressed as the angular distance from the pericenter which a fictitious body would have if it moved in a perfectly circular orbit in the same orbital period as the actual body in its elliptical orbit. The mean anomaly does not correspond to a real geometric angle, as does the true anomaly, but is a contrived parameter used to make calculating the position of the orbiting body in the two-body problem mathematically convenient.
meridian
    A line running north–south across the sky and passing through the point directly overhead known as the zenith.
Messier object
    One of a set of 110 "nebulous" astronomical objects, of which 103 were catalogued by French comet hunter Charles Messier between 1771 and 1781.
meteor

Also called a shooting star or falling star.
    The visible passage of a glowing meteoroid, micrometeoroid, comet, or asteroid through the Earth's atmosphere, usually as a long streak of light produced when such an object is heated to incandescence by collisions with air molecules in the upper atmosphere, leaving an ionization trail as a result of its rapid motion and sometimes also the shedding of material in its wake.
meteorite
    A solid piece of debris from a meteor that originated in outer space and survived its passage through the atmosphere to reach the surface of a planet or moon.
meteoroid
    A small rock or boulder that has entered a planetary atmosphere. If it survives to reach the surface, it is then termed a meteorite.
meteor shower
    A series of meteors that seemingly radiate from a single area in the night sky. These are produced by debris left over from a larger body, such as a comet, and hence they follow roughly the same orbit. This makes many meteor showers predictable events, as they recur every year.
metallicity
    A measure of the abundance of elements other than hydrogen and helium within an astronomical object. Note that this definition includes elements that are not traditionally considered metallic by chemical convention.
micrometeorite
    A very small meteorite that has survived its passage through the atmosphere to reach the surface of a planet or moon, usually ranging in size from 50 µm to 2 mm. Micrometeorites are a major component of cosmic dust.
micrometeoroid
    A very small meteoroid, usually weighing less than one gram. If it survives to reach a planetary surface, it is then termed a micrometeorite.
microvariable
    A stellar object such as a variable star that undergoes very small variations in luminosity. Detecting microvariability typically requires a sufficient number of observations to rule out random error as a source.[12]
Milky Way
    The Milky Way is the galaxy that contains our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye.
minor planet
    An object in direct orbit around the Sun that is neither a dominant planet nor originally classified as a comet. A moon is not a minor planet because it orbits another body instead of the Sun.
molecular cloud
    An interstellar cloud in which the prevailing physical conditions allow molecules to form, including molecular hydrogen.
moment of inertia factor

Also called the normalized polar moment of inertia.
moon
    See natural satellite.
Moon
    The solid, rocky body that orbits the Earth as its only natural satellite, completing a full orbit every 27.3 days. The Moon's gravitational influence is responsible for tides on Earth; because of tidal locking, only one side of the Moon is ever visible from the Earth. Sunlight reflected from its surface makes the Moon appear very bright in the night sky, though its orbital position with respect to the Earth and the Sun causes its visibility to change in a regular cycle of phases when viewed from the Earth. The adjectival lunar is often used to specifically describe the orbit, gravity, and other properties of the Earth's Moon.
moonlet
Morgan–Keenan classification system

Also called the MK classification.
morning width

Also called rise width.
    The horizontal angular distance between the rise azimuth of a celestial body and the east direction.[13][14][15]
moving group

Also called a stellar association.
    A loose grouping of stars which travel together through space. Although the members were formed together in the same molecular cloud, they have since moved too far apart to be gravitationally bound as a cluster.
multi-messenger astronomy
    A type of astronomy based on the acquisition of information about astronomical objects by the coordinated observation and interpretation of disparate classes of "messenger" signals with extrasolar origins: electromagnetic radiation, gravitational waves, neutrinos, and cosmic rays. Because these four extrasolar messengers are created by different astrophysical processes, their presence or absence during a celestial event can reveal useful information about their sources.
multiverse

N

natural satellite

Also called a moon.
    Any astronomical body that orbits a planet, minor planet, or sometimes another small Solar System body.
near-Earth object (NEO)
    Any small Solar System body, such as an asteroid or comet, whose orbit brings it into proximity with Earth, generally by being less than 1.3 AU from the Sun at its closest approach.
nebula
    Any astronomical object of indistinct nebulosity. In modern usage, the term typically refers to an interstellar cloud of dust, hydrogen, helium, and other ionized gases. Historically, it was also used to refer to extended sources of luminosity that could not be resolved into their individual components, such as star clusters and galaxies.
neutrino
neutron star
    A type of compact star that is composed almost entirely of neutrons, which are a type of subatomic particle with no electrical charge. Typically, neutron stars have a mass between about 1.35 and 2.0 times the mass of the Sun, but with a radius of only 12 km (7.5 mi), making them among the densest known objects in the universe.
New General Catalogue (NGC)
night sky
    The appearance of the Earth's sky at nighttime, when the Sun is below the horizon, and more specifically when clear weather and low levels of ambient light permit visibility of celestial objects such as stars, planets, and the Moon. The night sky remains a fundamental setting for both amateur and professional observational astronomy.
non-inclined orbit
    Any orbit that is coplanar with a specified plane of reference, such that the orbital inclination is 0 degrees for prograde orbits and 180 degrees for retrograde ones.
nuclear star cluster (NSC)
number density
    The quantity of some specified particle or object class per unit volume. For atoms, molecules, or subatomic particles, the volume is typically in cm−3 or m−3. With stars, cubic parsecs (pc−3) are often used.
nutation
    A continuous, gravity-induced change in the orientation of an astronomical body's axis of rotation which results from the combined effects of small, short-term variations. Nutation is distinguished from precession, which is a similar but longer-term change in axial orientation.

O
OB association
    A group of massive stars which are not gravitationally bound to each other, but move together through space in a loose association. The OB in the name is a reference to stars of stellar classifications O and B.
obliquity
    See axial tilt.
observable universe
observational astronomy
    The practice and study of directly observing astronomical objects with the use of telescopes and other astronomical instruments. It is concerned with recording data about the observable universe, as opposed to theoretical astronomy, which is concerned with calculating the measurable implications of astronomical models.
occultation
    A celestial event that occurs when a distant astronomical body or object is hidden by another, nearer body or object that passes between it and the observer, thereby blocking the first object from view. Solar and lunar eclipses are specific types of occultations.
Oort cloud

Also called the Öpik–Oort cloud.
    A vast theoretical cloud of predominantly icy planetesimals hypothesized to surround the Sun at distances ranging from 2,000 to 200,000 AU. It is thought to be divided into two regions: a disc-shaped inner Oort cloud and a spherical outer Oort cloud. The outer limit of the Oort cloud is often considered the cosmographical boundary of the Solar System.
opacity
    A measure of the resistance of a medium to the radiative transmission of energy. Within a star, it is an important factor in determining whether convection occurs.
open cluster
    A gravitationally bound group of up to one thousand stars that formed together in the same molecular cloud.
opposition
    The positioning of two celestial objects on opposite sides of the sky, from the perspective of an observer. This occurs, for example, when a planet makes its closest approach to the Earth, placing it in opposition to the Sun.
orbit
    The gravitationally curved trajectory of an object, such as the trajectory of a planet around a star or a natural satellite around a planet. Though the smaller body is often said to orbit the larger body itself, both bodies actually follow approximately elliptical orbits around a common center of mass positioned at a focal point of each ellipse. The word "orbit" can variously refer to the elliptical trajectory itself or the act of following this trajectory, and can refer to a stable, regularly repeating trajectory as well as a non-repeating trajectory.
orbit plot

Also called orbital plot.
    A schematic diagram of a complete orbit. For a binary system, it is typically presented from the primary's frame of reference.[16]
orbital eccentricity
    A parameter that determines how much an orbit deviates from a perfect circle. For an elliptical orbit, the eccentricity ranges from greater than zero to less than one.
orbital elements
    The set of parameters that uniquely define an orbit.

A diagram showing four of the six canonical orbital elements. The orbital plane (yellow) intersects a reference plane (grey).
orbital inclination
    The tilt of an object's orbit around an astronomical body, expressed as the angle between the orbital plane or axis of direction of the orbiting object and a plane of reference.
orbital mechanics
orbital node
    One of two points at which the plane of an orbit intersects a specified plane of reference to which it is inclined; in some contexts, the two nodes may be distinguished as the ascending node and the descending node. A non-inclined orbit, which is coplanar with the reference plane, has no nodes.
orbital period
    The time a given astronomical object takes to complete one orbit around another object. For objects in the Solar System, the orbital period is often referred to as the sidereal period.
orbital plane
    The imaginary geometric plane defined by the orbit of an astronomical body around its primary. The Earth's orbital plane, which defines the ecliptic, is commonly used as a plane of reference for the orbits of other objects in the Solar System.
orbital resonance
orbital speed
    The speed at which an astronomical body or object orbits around a barycenter, or its speed relative to the center of mass of the most massive body in the system. The term may be used to refer to either the mean orbital speed, i.e. the average speed over the entire orbital period, or the instantaneous speed at a particular point in the orbit. Maximum instantaneous orbital speed typically occurs at periapsis.
origin of longitude
osculating orbit
    The hypothetical, idealized Kepler orbit that an orbiting object would follow around its primary if all perturbations were absent, i.e. the orbit that coincides with the instantaneous orbital state vectors at a given moment in time.[17]
outer space

Also simply called space.
    The vast, nearly empty expanse that exists beyond the Earth and between all celestial bodies, characterized generally by extremely low densities of particles, extremely low temperatures, and minimal gravity. Most of the volume of the Universe is intergalactic space, and even galaxies and star systems consist almost entirely of empty space.

P

The parallax shift of a star at a distance of one parsec as seen from the Earth (not to scale)
parsec (pc)
    A unit of length defined as the distance at which a star would show a parallax shift of exactly one arcsecond as observed from Earth's orbit. It is equal to 3.2616 light-years or 206,265 astronomical units. The word "parsec" is a portmanteau of the words parallax and second.
partial solar eclipse
periapsis

Also called the pericenter.
    The point at which an orbiting body is closest to its primary. Contrast apoapsis.
perigee
    The point at which a body orbiting the Earth (such as the Moon or an artificial satellite) is closest to the Earth. Contrast apogee.
perihelion
    The point at which a body orbiting the Earth's Sun is closest to the Sun. Contrast aphelion.
perturbation
    The complex motion of an astronomical body that is subject to forces other than the gravitational attraction of its primary alone, or any force which complicates the orbital characteristics of the body such that the idealized Kepler orbit of the two-body problem is not an accurate representation of the body's actual orbit. Perturbing forces may include the gravitational forces exerted by any number of additional bodies, the off-center gravitational forces which are consequences of bodies not being perfectly spherical, and/or atmospheric resistance.
phase angle
    The elongation or angle between an orbiting body and the Sun as viewed from a particular perspective such as the Earth. It determines the amount of a planet or moon's visible surface that lies in shadow. Inferior planets such as Venus generally have low phase angles as seen from Earth, so they are often viewed as a crescent; superior planets such as Mars and Jupiter usually have high phase angles, so that little of the shadowed side is visible.
photometric system
photosphere
plane of reference

Also called a reference plane.
    An arbitrarily chosen, imaginary plane from which to measure and define orbital elements such as inclination and longitude of the ascending node. The ecliptic plane, invariable plane, and equatorial plane are all commonly used as reference planes in various contexts.
planet
    A type of astronomical body orbiting a star or stellar remnant which is massive enough to be rounded by its own gravity (but not massive enough to achieve thermonuclear fusion) and has cleared its neighbouring region of all planetesimals.
planetary
    Of or relating to a planet or planets.
planetary body

Also called a planetary object.
    Any secondary body that is geologically differentiated or in hydrostatic equilibrium and therefore has a planet-like geology, such as a planet, dwarf planet, or other planetary-mass object, but excluding smaller objects such as planetesimals.
planetary differentiation
    The process of separating out different constituents of a planetary body, causing it to develop compositionally distinct layers (such as a metallic core).
planetary nebula
    A type of emission nebula formed from a glowing shell of expanding plasma that has been ejected from a red giant star late in its life. The name derives from their resemblance to a planet. An example is the Ring Nebula.
planetary science

Also sometimes called planetology.
planetary system
    Any set of gravitationally bound non-stellar objects in or out of orbit around a star or star system. In general, planetary systems include one or more planets, though such systems may also consist of dwarf planets, moons, asteroids, meteoroids, planetesimals, and debris discs, among other objects.
planetary-mass object (PMO)

Also called a planemo or planetary body.
planetesimal
    Any solid object (generally larger than 1 kilometre (0.62 mi) in diameter) that arises during the formation of a planet whose internal strength is dominated by self-gravity and whose orbital dynamics are not significantly affected by gas drag. The term is most commonly applied to small bodies thought to exist in protoplanetary disks and debris disks during the process of planet formation, but is also sometimes used to refer to various types of small Solar System bodies which are left over from the formation process. There is no precise distinction between a planetesimal and a protoplanet.
planetoid
    Another name for a minor planet or dwarf planet.
polar orbit
    An orbit in which the orbiting object passes directly over or nearly over both poles of the body being orbited during each revolution. It therefore has an inclination equal or nearly equal to 90 degrees to the body's equator.
precession
    Any slow change in the orientation of an object's axis of rotation. For the Earth in particular, this phenomenon is referred to as the precession of the equinoxes. Apsidal precession refers to a steady change in the orientation of an orbit, such as the precession in the orbit of Mercury that was explained by the theory of general relativity.
precession of the equinoxes
primary

Also called a gravitational primary, primary body, or central body.
    The main physical body of a gravitationally bound, multi-object system. The primary constitutes most of the system's mass and is generally located near the system's barycenter.
prograde motion

Also called direct motion.
    Orbital or rotational motion of an object in the same direction as the rotation of the object's primary. The direction of rotation is determined by an inertial frame of reference such as the fixed stars. Contrast retrograde motion.
projected separation
    The minimum physical separation between two astronomical objects, as determined from their angular separation and estimated distance.[18] For planets and double stars, this distance is usually given in astronomical units. The actual separation of the two objects depends on the angle of the line between the two objects to the line-of-sight of the observer.
proper motion
    The rate of angular motion of an object over an interval of time, usually years. For stars, this is typically given in milliarcseconds per year.
protoplanet
    A large planetary embryo that originated within a protoplanetary disk and has since undergone internal melting to produce an interior of non-uniform composition. Protoplanets represent an intermediate step in the formation of a full-sized planet; they are thought to form out of smaller planetesimals as they collide with each other and gradually coalesce into larger bodies.
protoplanetary disk
protostar
    A concentration of mass formed out of the contraction of a collapsing interstellar cloud. Once sufficient mass has fallen onto this central core, it becomes a pre-main-sequence star.
pulsar
    A highly magnetized rotating neutron star or white dwarf that emits a beam of electromagnetic radiation. This beam is observed only when it is pointing toward Earth, making the object appear to pulse.

Q

quadratic field strength
    A method of computing the mean strength of a varying stellar magnetic field. It is determined by calculating the root mean square of a series of longitudinal magnetic field strength measurements taken at different times.[19]
quasar

Also called a quasi-stellar radio source
    A distant, point-like energy source originating from a powerful active galactic nucleus. Its luminosity is generated by the accretion of gas onto a supermassive black hole. Quasars emit radiation across the electromagnetic spectrum from radio waves to X-rays, and their ultraviolet and optical spectra are characterized by strong, broad emission lines.

R
radial velocity
    The velocity of an object along the line of sight to the observer, which in astronomy is usually determined via Doppler spectroscopy. Positive values are used to indicate a receding object. An object such as a star can undergo changes in its radial velocity because of the gravitational perturbation of another body, or because of radial pulsations of its surface. The latter, for example, occurs with a Beta Cephei variable star.
radio astronomy
    The subfield of astronomy that studies astronomical objects at radio frequencies, using large radio antennas known as radio telescopes.
radio source
    Any astronomical object that emits strong radio waves into space. These objects are the basis for radio astronomy.
red-giant branch
    A conspicuous trail of enlarged red stars found on the Hertzsprung–Russell diagram for a typical globular cluster. It begins at the main sequence turnoff point and extends toward the higher luminosity and lower temperature range until reaching the red-giant tip. This branch consists of older stars that have evolved away from the main sequence but have not yet initiated helium fusion in their core region.
redshift
regular moon
    A natural satellite following a relatively close and prograde orbit with little or no orbital inclination or orbital eccentricity. Regular moons are thought to form in situ about their primary, as opposed to irregular moons, which are thought to be captured.
relativistic jet
retrograde motion
    Orbital or rotational motion of an object in the direction opposite the rotation of the object's primary. The direction of rotation is determined by an inertial frame of reference such as the fixed stars. Contrast prograde motion.

In a retrograde orbit, a satellite (red) orbits in the direction opposite the rotation of its primary (blue/black)
right ascension
    In the equatorial coordinate system, the celestial equivalent of terrestrial longitude. It divides the celestial equator into 24 hours, each of 60 minutes.
ring system
    A disk- or ring-shaped accumulation of various solid material such as dust and moonlets that orbits an astronomical body such as a planet. Ring systems are common components of satellite systems around giant planets, as with the Rings of Saturn. See also circumplanetary disk.
Roche limit
    The distance from an astronomical object at which the tidal force matches an orbiting body's gravitational self-attraction. Inside this limit, the tidal forces will cause the orbiting body to disintegrate, usually to disperse and form a ring. Outside this limit, loose material will tend to coalesce.
rogue planet

Also called an interstellar planet, nomad planet, orphan planet, and starless planet.
    Any planetary-mass object that orbits a galactic center directly rather than a star or substellar object. Such objects have often been ejected from the planetary system in which they formed, or otherwise have never been gravitationally bound to any star system.
Rosseland optical depth
    An extinction coefficient of an atmosphere, which describes the net opacity to radiation at a given depth. See optical depth.[20]
rotation period
    The time that an object takes to complete a single revolution about its own axis of rotation relative to the background stars. It is not necessarily the same as the object's synodic day or sidereal day.
rotational modulation
    A phenomenon which causes the luminosity of a star to vary as rotation carries star spots or other localized activity across the line of sight. Examples include RS CVn and BY Dra variables.[21]

S

Saber's beads
    A broken arc of illuminations seen at the limb of very young or very old lunar crescents. The visual similarity to the moments before and after a total solar eclipse was first noted by American astronomer Stephen Saber.
satellite galaxy
scattered disc
secular motion
    Any change in movement that happens over a very long time period.[22] Examples include the perihelion precession of Mercury, the tidal acceleration of the Earth–Moon system, and precession of the Earth's axis.
semi-major axis

Also major semi-axis.
    One half of the longest diameter (the major axis) of an ellipse. It is expressed in units of length and often used to give a physical dimension to a two-body elliptical Kepler orbit, such as for a binary star system or star–planet system. When the distance between the orbiting bodies is unknown, the semi-major axis may be given as an angle.
September equinox

Also called the Southward equinox.
    The precise time of year on Earth when the Sun appears to cross the celestial equator, while generally trending southward at each zenith passage. It represents the moment at which the North Pole of the Earth begins to tilt away from the Sun, and typically occurs on or near September 22 each year. It is the autumnal equinox in the Northern Hemisphere and the vernal equinox in the Southern Hemisphere. Contrast March equinox.
sidereal day
sidereal period
    The orbital period of an object within the Solar System, such as the Earth's orbital period around the Sun. The name "sidereal" implies that the object returns to the same position relative to the fixed stars of the celestial sphere as observed from the Earth.
sidereal time
sidereal year
sky
    Everything that lies above the surface of the Earth, including the atmosphere and outer space. In the context of astronomy, the term "sky" is also used as another name for the celestial sphere. See also night sky.
small Solar System body (SSSB)
solar eclipse
solar flare
solar mass (M☉)
    A standard unit of mass equal to the mass of the Earth's Sun, or approximately 1.98847×1030 kg. It is commonly used to express the masses of other stars and astronomical objects relative to the Sun.
solar prominence
    A large, bright, transient feature, often in the shape of a loop, consisting of plasma extending outward from the Sun's photosphere into the corona. Prominences may be hundreds of thousands of kilometers long.
solar radius (R☉)
    A standard unit of distance equal to the radius of the Earth's Sun (typically measured from the Sun's center to the layer in the photosphere at which the optical depth equals 2/3), or approximately 695,700 kilometres (432,300 mi). It is commonly used to express the radii of other stars and astronomical objects relative to the Sun.
Solar System
    The gravitationally bound planetary system of the Earth's Sun and the objects that orbit it, either directly or indirectly, including the eight true planets, five dwarf planets, and numerous small Solar System bodies such as asteroids, comets, and natural satellites.
solar time
solar wind
solstice
    One of two precise times of year when the Sun reaches either its most northerly or most southerly point in the sky as seen from Earth. The solstices occur on or near June 20 and December 21 each year. The "Summer Solstice", often used to refer to the June solstice because of its occurrence during the Northern Hemisphere's summer, is the annual date featuring the longest duration of daylight and the shortest duration of nighttime in the Northern Hemisphere. The reverse is true for the "Winter Solstice", which is often used to refer to the December solstice.
spectroscopic binary
    A type of binary star system where the individual components have not been resolved with a telescope. Instead, the evidence for the binarity comes from shifts observed in the spectrum. This is caused by the Doppler effect as the radial velocity of the components change over the course of each orbit.
spectroscopy
speed of light
spherical astronomy

Also called positional astronomy.
    A branch of observational astronomy which is used to locate the positions of astronomical objects on the celestial sphere as they would appear from a particular date, time, and location on Earth. It relies on the mathematical methods of spherical geometry and the measurements of astrometry.
spiral galaxy
standard gravity (ɡ0 or ɡn)

Also called standard acceleration due to gravity.
    The nominal gravitational acceleration of an object in a vacuum near the surface of the Earth, as a result of Earth's gravity and, less importantly, the centrifugal force generated by its rotation. It is by definition equal to 9.80665 m/s2 (approximately 32.17405 ft/s2).
star
    A massive, luminous spheroid of plasma held together by its own gravity which, for at least a portion of its life, radiates energy into outer space due to the thermonuclear fusion of hydrogen into helium within its core. Astronomers can determine the mass, age, temperature, chemical composition, and many other properties of a star by observing its motion through space, its luminosity, and its emission spectrum.
star catalogue

Also spelled star catalog.
star cluster
star system

Also called a stellar system.
    Any small number of stars that orbit each other, bound by gravitational attraction, such as a binary star system. In the broadest sense, very large groups of stars bound by gravitation such as star clusters and galaxies are also star systems. Star systems are distinct from planetary systems, which include planets and other bodies such as comets.
starburst galaxy
    Any galaxy that has an anomalously high rate of star formation. The criteria for a starburst is a star formation rate that would normally consume the galaxy's available supply of unbound gas within a time period shorter than the age of the galaxy. Most starbursts occur as a result of galactic interactions, such as a merger.
starfield
    Any set of stars visible in an arbitrarily sized field of view of a telescope, usually in the context of some region of interest within the celestial sphere.[23][24] For example, the starfield surrounding the stars Betelgeuse and Rigel could be defined as encompassing some or all of the Orion constellation.
stellar
    Of or relating to a star or star system.
stellar atmosphere

Also called the stellar envelope.
    The outermost region of a star. Although it forms only a small portion of the star's mass, for some evolved stars the stellar envelope can form a significant fraction of the radius.
stellar classification

Also called spectral classification.
    The categorization of stars based upon their spectra. The modern MK spectral classification scheme is a two-dimensional classification based on temperature and luminosity.
stellar designation
stellar dynamics
stellar evolution
stellar evolution model

Also simply called a stellar model.
    An astrophysical model of a star's stellar evolution over time based upon its mass and chemical composition.[25]
stellar magnetic field
stellar parallax
stellar remnant
submillimetre astronomy
    The subfield of astronomy that studies astronomical objects detectable at submillimetre wavelengths (i.e. terahertz radiation).
subsatellite
    Any natural or artificial satellite that orbits another natural satellite, i.e. "a moon of a moon".
substellar object

Also called a substar.
    An astronomical object whose mass is smaller than the smallest mass at which the fusion of hydrogen nuclei can be sustained (equivalent to approximately 0.08 solar masses), including brown dwarfs and some stellar remnants, as well as certain planetary-mass objects.
Sun
supercluster
superior planet
    An archaic term that is sometimes used to refer to planets that orbit further from the Sun than the Earth, such as Saturn. The name originated from the geocentric cosmology of Ptolemy. Contrast inferior planet.
supermassive black hole (SMBH)
    One of a class of very large black holes which possess masses ranging from hundreds of thousands to many billions of times the mass of the Sun. These are typically found at a galactic core, where they can have a profound effect upon the evolution of the surrounding galaxy.
supernova
    An extremely luminous, transient stellar explosion occurring during a massive star's final evolutionary stages or when a white dwarf is triggered into runaway nuclear fusion.
surface gravity (g)
    The gravitational acceleration experienced at the equatorial surface of an astronomical body or other object, including that produced by the effects of rotation. It is typically expressed in units of acceleration such as meters per second squared (m/s2) or as a multiple of the Earth's standard gravity, which is equal to 9.80665 m/s2.
synchronous orbit
    Any orbit in which an object orbits its primary with an orbital period equal to the average rotational period of the primary and in the same direction as the primary's rotation.
synodic day
    The time it takes for an object to rotate once about its own axis (e.g. its rotation period) relative to the primary it is orbiting (rather than to distant fixed stars). The synodic day may be described as the time between two consecutive sunrises (in the case where the primary is a star), which is not necessarily the same as the sidereal day. An object's synodic day may change slightly in duration over the course of the orbital period due to eccentricity and axial tilt. For Earth, the synodic day is often called a solar day.
synodic period
    The time it takes for a body visible from another body (often the Earth) to complete a cycle with respect to the background stars visible in the second body's celestial sphere. Synodic period is most commonly used to indicate the elapsed time between a given body's consecutive appearances in the same location in the night sky as observed from Earth, but can in principle be calculated with respect to the sky as observed from any body. It is related to but distinct from the orbital period, a result of the fact that both the body being studied (e.g. Jupiter) and the body from which it is being observed (e.g. Earth) are independently orbiting a third body (the Sun).
syzygy
    The straight-line configuration of three celestial bodies in a gravitational system.

T
telescope
telluric star
    A star with nearly featureless continuum spectra that can be used to correct for the effect of telluric contamination of the Earth's atmosphere on the spectra of other stars. For example, water vapor in the atmosphere creates significant telluric absorption bands at wavelengths above 6800 Å. These features need to be corrected for in order to more accurately measure the spectrum.[26]
termination shock
    The boundary within the heliosphere, approximately 75 to 90 AU from the Sun, beyond which the solar wind slows to subsonic speeds (relative to the Sun) as a result of interactions with the local interstellar medium.
terminator
    The line that divides the illuminated side of a moon or planet from its dark side. The line moves as the object rotates with respect to its parent star.
theoretical astronomy
thick disk population
thin disk population
    The layer of the Milky Way galaxy where the spiral arms are found and where most of the star formation takes place. It is about 300–400 parsecs (980–1,300 light-years) deep and centered on the galactic plane. Stars belonging to this population generally follow orbits that lie close to this plane.[27] This is in contrast to members of the thick disk population and halo stars.
tidal braking

Also called tidal acceleration.
    The transfer of momentum between an astronomical body and an orbiting satellite as the result of tidal forces. This can cause changes in the rotation periods for both bodies as well as modification of their mutual orbit. A satellite in a prograde orbit will gradually recede from its primary while slowing the rotation rate of both bodies.
tidal force
tidal locking
    The net result of continued tidal braking such that, over the course of an orbit, there is no net transfer of angular momentum between an astronomical body and its gravitational partner. When the orbital eccentricity is low, the result is that the satellite orbits with the same face always pointed toward its primary.[28] An example is the Moon, which is tidally locked with the Earth.
tidal stream
    A stream of stars and gases which are stripped from gas clouds and star clusters because of interaction with the gravitational field of a galaxy such as the Milky Way.[29]
tilt erosion
    The gradual reduction of the obliquity of an orbiting satellite due to tidal interactions.[30]
total solar eclipse

A total solar eclipse as seen from Earth
trans-Neptunian object (TNO)
transit
    An astronomical event during which a body or object passes visibly across the face of a much larger body. An example is the transit of Venus across the face of the Sun, which was visible from Earth in 2004 and 2012. Because a transit results in a decrease in the net luminosity from the two objects, the transit method can be used to detect extrasolar planets as they pass in front of their host stars. A transit by an object that appears roughly the same size or larger than the body it is transiting is called an occultation or eclipse.
trojan
tropical year
true anomaly (ν, θ, or f)
    The angle between the direction of periapsis and the current position of an orbiting body as it moves along an elliptical orbit, as measured from the nearest focus of the ellipse. The true anomaly is one of three angular parameters that define a position along an orbital path, the other two being the eccentric anomaly and the mean anomaly, and also one of six canonical orbital elements used to characterize an orbit.
Tully–Fisher relation
    An empirical relationship between the mass or intrinsic luminosity of a spiral galaxy and its angular velocity or emission line width. It can be used to estimate the distance of the galaxy, and hence forms a rung on the cosmic distance ladder.
two-body problem

U

UBV photometric system

Also called the Johnson system or Johnson–Morgan system.
universe
    1.  The entirety of space and time and their contents, including galaxies, stars, planets, all other forms of matter and energy, and the physical laws and constants that describe them. When not otherwise qualified, "the Universe" usually refers to the entire Universe, whose spatial extent is unknown because it is not directly measurable; this is distinguished from the observable universe, whose size it is possible to measure.
    2.  One of many hypothetical parallel universes which exist as causally disconnected constituent parts of a larger multiverse, which itself comprises all of space and time and their contents.

V

variable star
    Any star that is observed to vary in brightness. This variation may be periodic, with one or more cycles that last hours, days, months, or even years. Some stars vary in an irregular manner, while others undergo cataclysmic changes in brightness. Other forms of variability are intrinsic changes to the star's radial velocity or its profile of spectral lines.
velocity dispersion
    The statistical dispersion of velocities about the mean velocity for a group of objects, such as stars in a globular cluster or galaxies in a galactic cluster. This value can be used to derive the combined mass of the group by using the virial theorem.
Virgo Supercluster (Virgo SC)

Also called the Local Supercluster (LSC or LC).

W

weak-line star
    A reference to the faintness of the spectral lines for a star compared to standard stars with the same stellar classification. Since most absorption lines are caused by elements other than hydrogen and helium—what astronomers refer to as "metals"—these are sometimes called metal weak stars.[31]
white dwarf
    A type of stellar remnant composed mostly of electron-degenerate matter. A white dwarf lacks the mass needed to continue the nuclear fusion process with its constituent atoms, so the object's energy output normally comes from radiative cooling. See nova and Type Ia supernova.
Wilson–Bappu effect
    A correlation between the width of the singly ionized calcium K-line (Ca II K) at 3933 Å and the absolute visual magnitude of the emitting late-type stars. This linear relation makes it useful for determining the distances of G, K, and M-type stars.[32]

X

XBONG

An acronym of X-ray bright optically normal galaxy.
    A seemingly normal galaxy that does not appear to have an active galactic nucleus, yet displays an anomalous level of excess X-ray emission.[33]

Z
zenith
    The point in the sky that is directly overhead from the perspective of a particular location on the Earth.
zero-age main sequence (ZAMS)
    The sequence of positions along the Hertzsprung–Russell diagram achieved by newly formed, chemically homogeneous stars which have finished contracting and have reached hydrostatic equilibrium, with energy being derived solely from nuclear fusion.[34]
zodiac
    The area of the sky that extends approximately 8 degrees north or south (in celestial latitude) of the ecliptic, the apparent path of the Sun across the celestial sphere over the course of the year as observed from Earth. The Sun, Moon, and visible planets appear to travel across a band of twelve Zodiac constellations within this belt as the Earth orbits the Sun.
zodiacal light

 

 

 30,000 foot view     Program management view
50,000 foot view     Highest management overview
Bandwidth     Availability[1]
Benchmark     Measuring against
Best practice     Tried and tested methodology/process
Blue sky thinking     Idealistic or visionary ideas, not always with practical application (source: BBC)
Bottleneck     Where a process is held up
Cascade     Array of possible actions to take in response to a problem: protocol
Check in the box     Complete the task
Cross-functional     Works in multiple directions simultaneously
Customer-centric     The customer is the main focus
Cutting edge practices     Up to date or new methods
Dashboard     Collection of key indicators
Deliverable(s)     Finished product or outcome
Downsize     Reduce the number of employees through a lay-off
End-user perspective     Point of view of a customer about a product or service
Evergreen     Content that is always relevant[1]
Flavour of the month     The current popular or trending activity
Golden handshake     Contract clause which richly rewards a key employee in the case of termination
Golden parachute     Contract clause richly (perhaps excessively) rewarding a key executive if termination is due to corporate takeover or merger
Hard stop     Deadline[1]
Hub     A central idea to which other ideas are linked
In the loop     Knowing what's going on and being kept informed
In the weeds     Immersed or entangled in details or complexities
Joined-up thinking     Discussing the viewpoints of each organization and coming to an agreement or compromise
Low-hanging fruit     Tasks that have the greatest positive effect for the least effort, used when promoting new projects to show the advantages.[1]
Lay-off     Redundancies on a large scale
Learnings     Acquired knowledge after an action/actions or process/processes has been completed
Nesting     Processes within processes
Off the shelf     Buying in a product or service that is already completed
One button to push/Push of a button     Reduced number of suppliers
Operational excellence     Sustainable improvement of key performance metrics
Python     Challenging problem[1]
Raft of measures     A collection of proposals or schemes
Rattler     Obvious problem[1]
Run it up the flagpole     Test the popularity of a new idea or proposal. [2]
Scalability     A small component's ability to grow within a larger system[1]
Silo (Vertical and Horizontal)     A system, process, department, etc. that operates in isolation from others.
Silver bullet     One solution for everything[dubious – discuss]
Six Sigma     A system for process improvement by error reduction
Stakeholders     Group or individual affected by the outcome of a decision
Talent     Employees
Tent pole     The task or item most likely to delay a project or consume the most resources
Under-pinning     The foundations of an idea, which helps another related scheme or proposal
Unique selling proposition (USP)     Any aspect of an object that differentiates it from similar objects
Win-win solution     Providing a product or service which makes everyone happy, particularly both buyer and seller
Verb phrases
Verb phrase     Definition
Action that     Put something into practice[1]
Baked in     Something which has been "baked in" is implied to be impossible to remove. Alternatively, "baked in" can refer to a desirable, although non-essential, property of a product being incorporated for the user's convenience.
Boil the ocean     Undertake an impossible or impractical task [1]
Buck the trend     To follow an action against market tendencies
Build capacity     Take actions which increase the amount of work that can be done in the future.
Circle back     Discuss later[1]
Circle the wagons     Defensive strategy to provide time to plan or produce a better solution
Cover all directions of the compass     Ensure the product specification covers everything
Create the storyboard     Outline what the solution will look like
Deep dive     Get into the detail
Drill down     Investigate in depth [1]
Flogging a dead horse     Wasting efforts[1]
Have the vendor in our pocket     Keep a vendor/contractors paid
Ideate     Come up with ideas[1]
Land and expand     To sell a small solution and then grow it within the client's environment
Make hay     Productive or successful in a short time[1]
Moving forward     Making progress on an idea or scheme
Move the goal posts     Change the criteria for success[1]
Pick the low-hanging fruit     Go (initially) for the easiest options [1]
Power to the elbow     Get additional backup information to make your case stronger
Pull the plug     Close a venture that is losing money or has no prospects of success
Punt     Relinquish responsibility[1]
Pushing the envelope     Going outside normal boundaries to achieve a target or goal (such as exceeding specifications)
Put this on your radar     Consider this[1]
Scrub the numbers     Find errors[1]
Sing from the same hymn sheet     Show a united front, or everyone understanding and saying the same thing to clientele.
Table the conversation     Reconvene at a later time[1]
Test the water     'Put your toe' into a market to determine its temperature.
Touch base     To meet up with a colleague to discuss progress (from baseball)
Touch base offline     Meet and talk[1]
Tranch up the workload     Divide responsibilities[1]
Trim the fat     Cut excess budgets, remove avoidable costs [1]
Unscramble that egg     Take care of that mess[1]

 

 A

AC adapter
    An external power supply for portable devices that allows them to operate from wall-socket electricity.
AC power plugs and sockets
    Electrical connectors used with alternating current.
AC power
    Electric power where the current reverses direction periodically.
AC/AC converter
    A power converter where the input and output are both alternating current, but may differ in frequency or other characteristics.
AC/DC receiver design
    A radio receiver that can operate from either alternating current or direct current wall socket power.
AC/DC conversion
    Rectification of AC current, so that current flows in only one direction.
active rectification
    A circuit where rectifier devices are externally controlled to change AC to current flowing in one direction.
actuator
    An end device of a control system, that manipulates a physical variable such as a valve opening or position of a machine part.
adaptive control
    A control strategy where parameters are adjusted as the controlled process changes.
additive white Gaussian noise
    A noise model that is used in telecommunications to model the effects of various random processes.
adjustable-speed drive
    Control for a motor that allows more than one speed to be selected.
advanced Z-transform
    A mathematical technique used to model and analyze digital systems.
affinity laws
    Mathematical formulas that relate the speed, flow, and diameter of pumps, fans, blowers, and turbines, useful for predicting output under varying conditions.
agbioeletric
    A brand name of a kind of vegetable oil for use in transformers.
AIEE
    American Institute of Electrical Engineers, predecessor organization to IEEE.
alpha–beta transformation
    A mathematical technique useful in analysis of three-phase circuits.
alternating current
    Electric current that reverses direction periodically.
alternator
    An electrical machine that converts mechanical power into AC electric power.
alternator synchronization
    The process of synchronizing an alternator to a grid or another alternator.
aluminium smelting
    Reduction of aluminium ore to metal, by use of large amounts of electric power.
ammeter
    An instrument that measures electric current.
amorphous metal transformer
    A power transformer where the metallic core is made of metals cooled so quickly that they do not form a crystal structure; such transformers can reduce some kinds of energy loss.
ampacity
    The current carrying capacity of a conductor, in the context of electric power wiring.
ampere
    The SI unit of electrical current.
Ampère's circuital law
    The mathematical relation between the integral of the magnetic field over some closed curve to the current passing through the region bound by the curve.
Ampère's force law
    The mathematical relation between the force between two current carrying conductors and the current flowing in them.
Ampère's law
    Ampère's circuital law.
amplidyne
    An electric machine that allows a small current to control a much larger current.
amplifier
    A system that produces an output that replicates an input signal but with a larger magnitude.
amplitude modulation
    Transmission of information by changing the magnitude of a carrier signal, for example sending sound by radio.
analog circuit
    A circuit where currents and voltages vary continually within some practical range, in proportion to some signal.
analog filter
    An analog circuit that alters some frequency-related property of a signal.
analog signal processing
    Generally, techniques used to alter signals that rely on voltages or currents that vary continually over a practical range.
analog signal
    A signal whose properties (current, voltage) vary proportionally to the information transmitted.
analog-to-digital converter
    A circuit that produces a number proportional to the magnitude of a voltage or current.
anode
    The terminal of an electrochemical or electronic device through which conventional current flows inward.
antenna
    A structure which converts between electromagnetic waves in space and currents in a conductor.
apparent power
    In an alternating current power circuit, the product of the magnitude of RMS voltage and current.
Apple Computer
    A company that makes mobile telephones and computers.
arbitrary waveform generator
    A type of signal generator that can generate almost any waveform.
arc converter
    A device once used to generate radio waves.
arc furnace
    A furnace that melts material by use of an electric arc.
arc lamp
    An electric lamp that generates light from an electric arc.
arc welder
    A device used to join metals by melting them with an electric arc.
armature
    That part of an electrical machine that converts electrical energy to mechanical energy (or vice versa).
artificial intelligence
    A computer system that replicates some feature of human intelligence.
artificial neural networks
    An electrical network that mimics the function of a biological nervous system.
asymptotic stability
    A condition of a control system where the output eventually reaches a steady-state value in response to any input.
asynchronous circuit
    A digital circuit where states propagate through a circuit without a synchronizing clock impulse.
audio and video connector
    An electrical fitting used to connect cables carrying audio or video signals.
audio equipment
    Equipment used to handle signals at frequencies within the human range of hearing.
audio filter
    A circuit intended to alter some frequency-related property of a signal carrying sound information.
audio frequency
    A signal whose frequency is within the range of human hearing.
audio noise reduction
    Reduction of interfering signals in an audio signal.
audio signal processing
    Alteration of any properties of a signal carrying sound information (dynamic range, frequency response, or others).
audion tube
    An early three electrode vacuum tube that had amplifying properties.
Austin transformer
    A kind of isolation transformer.
automatic gain control
    A circuit that automatically adjusts the magnitude of a signal to prevent it from becoming too small or too large.
automatic transfer switch
    An electrical switch used to automatically select a standby source of electrical power when the principal source is lost.
automation
    Automatic control of a process.
autorecloser
    A circuit protection device for overhead power distribution lines which briefly interrupts a circuit when a fault is detected, then restores the circuit in the expectation the fault has cleared.
autotransformer
    A transformer where the primary and secondary circuits share some of the transformer windings.
availability factor
    The fraction of time that a power plant is available to produce power.
avalanche diode
    A diode intended for regular operation in the reverse, avalanche breakdown, mode. Used as a voltage reference, noise source, and in certain classes of microwave oscillator device.
average rectified value
    The average value of an alternating current waveform, taking the absolute value of the waveform. The average value is generally different from the root-mean-square value.



B

backward wave oscillator
    A type of microwave oscillator vacuum tube.
balanced line
    A transmission line with two conductors, with equal impedances to earth ground.
ball bearing motor
    A conceptual motor that does not use electro-magnetism.
balun
    A device that connects a balanced transmission line to an unbalanced line.
band-pass filter
    A filter that lets through signals within a range of frequencies.
band-stop filter
    A filter that blocks signals with a particular range of frequencies.
bandwidth
    The range of frequencies over which a system generates or uses significant signal power.
bang-bang control
    A controller that switches a final element on or off instead of providing a proportional response.
Barlow's wheel
    A demonstration of electromagnetic principles.
Bartlett's bisection theorem
    A mathematical theorem used in network analysis.
base load power plant
    An electric power plant that furnishes the part of load that does not vary during a day.
battery
    An electrochemical device that produces electric power from chemical reactions.
battery eliminator
    An AC adapter, which allows battery operated equipment to run on wall-socket AC power.
Bayer filter
    An optical filter used in color digital cameras.
beam tetrode
    A type of vacuum tube with four active elements plus a pair of beam forming plates.
beat frequency
    A frequency produced by non-linear mixing of signals at two other frequencies.
Bell Telephone Laboratories
    Formerly, the research and development laboratory of the American Telephone and Telegraph Corporation.
biasing
    The practice of setting the quiescent operating conditions of an amplifying device to obtain desired response.
BIBO stability
    A control system that produces finite outputs for any finite input.
bilinear transform
    A mathematical technique to obtain the parameters for a digital filter to duplicate the response of some analog filter transfer function.
bimetallic strip
    A temperature sensing element made of two metals that have different coefficients of expansion intimately bonded together.
Biot–Savart law
    The mathematical relationship between a magnetic field and the current producing that field.
bipolar junction transistor
    A type of transistor with two kinds of charge carriers.
blocked rotor test
    A test of an electric machine where the machine is energized but the shaft is prevented from turning.
Blu-ray
    A type of optical disc written and read using a blue/violet laser.
Bode plot
    A plot of the amplitude and phase frequency response of a system, where the actual response is approximated by straight line segments.
Boolean algebra (logic)
    A type of algebra that deals with values that can only hold values "true" and "false", of great use in design and analysis of digital systems.
boost converter
    Any power converter circuit that can produce an output voltage larger than its input voltage.
booster
    A device used to increase voltage on an electric power distribution system, such as a motor-generator set on a DC system.
bound charge
    Electric charge in a material that is not free to move through the material.
braking chopper
    A device used to absorb energy from a motor to slow it down.
branch circuit
    In building wiring, any circuit from the main panelboard to utilization equipment or receptacles.
breakdown voltage
    The maximum voltage a device can withstand without damage.
bridge rectifier
    A set of rectifier diodes used to convert alternating current to direct current.
broadcasting
    Transmission of a signal to many receivers.
brush
    A sliding electrical contact between a moving part and a stationary part.
brushed DC electric motor
    An electric motor with brushes.
brushless DC electric motor
    An electric motor without brushes.
Buchholz relay
    A gas pressure sensing device for protection of oil-filled transformers.
Buck converter
    Any power converter circuit that produces an output voltage less than its input voltage.
Buck–boost converter
    Any power converter circuit that can provide a voltage greater or less than its input voltage.
Buck–boost transformer
    A transformer that can be used to adjust voltage.
busbar
    A set of conductors used to distribute current to many branches.
bushing
    An electrical fitting used to connect external conductors to the interior of apparatus.
Butterworth filter
    A type of filter with the flattest possible pass band.
buzzer
    An electromechanical or electronic device that produces a sound when energized.

Contents:

    Top 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

C

Canadian Electrical Code
    The technical standard for building wiring in Canada.
Canadian Standards Association
    Non-profit organization that develops electrical and other technical standards.
capacitance
    The ability of a body to hold an electrical charge.
capacitor
    An electrical component that stores energy in an electric field.
capacitor-input filter
    A power supply network where a capacitor is the first element following the rectifier.
capacitor voltage transformer
    In electrical power systems, an instrument transformer for measuring voltage that uses a capacitive voltage divider.
capacity factor
    The ratio of energy produced by a power plant over some period, over its maximum possible energy production in that time.
carrier current
    A system for communications where a carrier signal is impressed on power line wiring.
carrier wave
    A radio wave that can be modulated (changed systematically) to carry information to a receiver.
Category 3 cable
    A performance standard for unshielded twisted pair cables for analog voice and low speed data circuits within a building.
Category 5e cable
    A performance standard for unshielded twisted pair cables for telephone and data within a building.
Category 6 cable
    A performance standard for unshielded twisted pair cables for telephone and high speed data within a building.
catenary
    A geometric form of curve, the shape of a uniform cable hanging between two supports.
cathode ray oscilloscope
    An electronic instrument that displays the wave shape of electrical signals on a cathode ray tube.
cathode ray tube
    A vacuum tube that relies on an electron beam – usually used to render images on a fluorescent screen such as in television sets.
cathode
    The terminal of an electrochemical or electronic device from which conventional current exits the device.
cat's-whisker detector
    A radio detector that uses a manually-set "whisker" contact to a crystal of galena or other material, to form a rectifying junction.
CATV
    Cable television, distribution of television programming over a wire instead of by radio broadcast.
cavity magnetron
    A vacuum tube that is a high power microwave oscillator, using a resonant cavity and electrons traveling through a magnetic field.
CCFL inverter
    A power supply to generate the voltages required to operate a cold cathode fluorescent lamp.
CD
    A "Compact Disc" used to store digital data or digitally recorded sound using an infrared laser.
center tap
    A connection on a transformer which has equal voltage to either end of the transformer winding.
ceramic resonator
    A piezoelectric element used to stabilize the frequency of an oscillator.
channel
    Any communication path between a signal transmitter and a signal receiver, or, a pre-selected operating frequency for a radio system.
channel capacity
    An upper bound on the rate at which information can be reliably transmitted over a communication channel.
charactron
    A kind of text display vacuum tube that used an internal element to shape an electron beam to represent the shape of letters and other symbols.
charge pump
    A DC to DC converter circuit that uses capacitors to store energy between stages.
charge transfer switch
    A kind of charge pump circuit.
charge-coupled device
    An imaging sensor or data storage device that represents a signal, or pixel, by the charge stored in a capacitor and is able to move that charge from one capacitor to the next.
Chebyshev filter
    A form of filter that has a steep frequency selective characteristic.
choke
    An induction coil used to block alternating current and pass direct current, or to block high frequencies and pass lower frequencies.
chopper
    A circuit that switches on and off at a high rate, used either for power conversion or to convert a DC signal to a more easily processed AC signal.
circle diagram
    A representation of the voltage and current characteristics of an electrical machine; the plot traces out a circle or part of a circle.
circuit breaker panel
    A distribution board for electric power that uses circuit breakers as protective elements.
circuit breaker
    An automatically operated electrical switch that opens to interrupt a short circuit or other fault.
circuit theory
    The mathematical theory of electrical circuits.
Circuit Total Limitation (CTL)
    A US National Electrical Code rule for the number of circuits in a panel board.
clamp meter
    An ammeter that measures current with a split core that can be clamped on a wire.
Clapp oscillator
    An electronic oscillator circuit that uses three capacitors and an inductor.
class of accuracy in electrical measurements
    A measure of the error produced by an electrical measuring instrument.
closed-loop controller
    Any controller that manipulates some process variable to minimize the difference between the current state of the variable and the desired set point, such as temperature, flow, or others.
CMOS
    Complementary metal–oxide–semiconductor, a fabrication process for MOSFETs and integrated circuits
coaxial cable
    A cable with an inner conductor centered inside a flexible tubular conductor, used for radio frequency transmission lines.
Cockcroft–Walton generator
    A kind of circuit for generating very high DC voltage.
cogeneration
    Production of electricity along with some other desired product, such as process steam or desalinated water.
cold cathode
    An element of a vacuum tube that emits electrons without a heating circuit.
Colossus
    A British code breaking system used during World War II.
combined cycle
    A thermal power plant that improves efficiency with two different kinds of energy extraction from the combustion products gas stream, such as a gas turbine followed by a steam boiler.
communication system
    A system intended to convey information from one place to another with an expected degree of performance.
communications satellite
    A satellite in Earth orbit designed for international telephone, television, or data transmission.
commutation cell
    The elementary switching device in a power converter circuit; it could be a transistor, a thyristor, a mercury-arc valve, or others.
commutator
    A component of a DC electric machine that connects the rotating coils with an external circuit through brushes.
compact fluorescent lamp
    A fluorescent lamp with a folded or spiral tube, designed to fit in the same space as an incandescent lamp of similar light output.
Compactron
    A brand of vacuum tube, used in some radio and television sets, that combined multiple independent functions in one envelope.
compensation winding
    A winding on a motor or generator to improve commutation at heavy load.
computed tomography
    Production of images of a cross-section through an object by multiple X-ray measurements processed in a computer.
computer engineering
    The profession of designing computers.
computer hardware
    That part of a computer system with physical existence.
computer programming
    The practice of producing instructions for a computer to achieve some desired effect.
computer-aided design (CAD)
    A design discipline where a computer is used to produce graphical representation of the design or to assist in calculating performance parameters.
conduction band
    In a conductor, the energy levels of charge carriers that are free to move through the material.
constant k filter
    A method formerly used for designing filters for a required characteristic.
consumer electronics
    Electronic devices intended to be owned by consumers directly; a mobile cell phone is "consumer electronics" but the cell site it communicates with is not.
contactor
    An automatically controlled electrical switch (relay), used to operate motors or other high-current loads.
continuous Fourier transform
    A mathematical operation that expresses a signal in time as the sum of its frequency components.
continuous signal
    A signal that can take any value within its range.
control engineering
    The application of control theory to practical problems.
control system
    The equipment used to adjust some parameter of an ongoing process to regulate its behavior to a desired goal, such as positioning a disk drive head or regulating temperature of a furnace.
control theory
    The mathematical study of behavior of control systems.
controllability
    In control theory, the degree to which a system can be put into any desired state given manipulation of one variable.
controller
    A system that adjusts some variable to control a process.
copper cable certification
    The process of testing a computer network cable installation to verify that it meets standards.
copper loss
    That portion of an electric machine or transformer's loss attributed to the resistance of conductors (which are not necessarily made of copper).
corona ring
    A component of a high-voltage system intended to smooth out the electric field distribution around energized parts.
coulomb
    The SI unit of electric charge.
Coulomb's law
    The mathematical relation between force, electric charge and distance.
CPU
    Central Processing Unit, the element of a computer that carries out arithmetic and logic operations.
crest factor
    The ratio of peak to effective (RMS) value of a waveform.
crossed-field amplifier
    A type of microwave amplifier vacuum tube.
crosstalk
    Objectionable presence of a signal from one circuit in another circuit sharing the same transmission path, such as a cable.
crystal oscillator
    An electronic oscillator whose frequency is stabilized by a piezoelectric crystal resonator element.
Ćuk converter
    One kind of buck-boost voltage converter that uses a capacitor as an energy storage element.
current
    The movement of electric charge.
current density
    The current flowing per unit area of a conductor.
current source inverter
    A type of power inverter where an inductor tends to keep a constant current flowing in the inverter stage.
current source
    In circuit theory, an element that produces a defined current independent of the connected circuit properties.
current transformer
    An instrument transformer used for measuring current in AC power systems.
current-to-voltage converter
    A transducer that produces an output voltage in response to an input current.
cybernetics
    The science of automatic control systems.
cycloconverter
    A type of variable-frequency power converter that does not first convert AC to DC.

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D

damping ratio
    A parameter that indicates how rapidly oscillations in a system die out, if ever.
Darlington transistor
    An interconnection of two transistors to provide a gain that is the product of the individual gains.
data compression
    Any technique that allows information to be transmitted more compactly than originally expressed, for example, codes.
data networks
    A network for interconnection of computers and peripherals.
DC injection braking
    A method of slowing an AC electric motor by passing direct current through its windings.
DC-to-DC converter
    A circuit that takes power from a DC source and generates a different DC voltage.
degaussing
    The process of reducing the residual magnetic field in a metallic object, such as a ship.
delay line
    A circuit component that introduces a delay in a signal.
delta-wye transformer
    One type of connection of a three-phase transformer.
demand factor
    The fraction of actual use of some quantity, related to the maximum that could be used in a specified time.
demand response
    The ability of a generating station or grid to follow changes in load while maintaining voltage and frequency within acceptable limits.
demodulation
    The process of recovery of information (sound, video, data) from a modulated carrier.
describing function
    A method for analyzing non-linear control systems.
detector
    A circuit that demodulates a radio signal to recover information.
DIAC
    A four-layer semiconductor diode that has a predictable breakdown characteristic.
dielectric
    A material that does not allow free flow of electric current.
digital audio broadcasting
    Transmission of sound by digital signals over radio.
digital circuit
    A circuit where all points on the signal path have only one of two states.
digital computers
    A computer made of digital circuits.
digital control
    A control system that processes signals in digital form.
digital filter
    A filter implemented as a digital circuit.
digital image processing
    Manipulation of an image by a digital computer.
digital micromirror device
    An element of a kind of digital projector system.
digital protective relay
    A power system protection device that processes signals in digital form.
digital signal controller
    A type of microprocessor that combines a digital signal processor element with a more general purpose microcontroller.
digital signal processing
    The technique of modifying the properties of a signal that has been converted to digital form.
digital television
    Transmission of images using digital techniques.
digital-to-analog converter
    A device that produces a voltage or current that is proportional to a digital value sent to it.
diode bridge
    An interconnection of diodes to rectify alternating current to direct current.
diode
    A two-terminal passive circuit element, with a preferred direction of current flow.
dipole antenna
    A simple form of antenna that consists of two conductors oriented end-to-end with a feed in between them.
direct current (DC)
    Electric current that flows in one direction only.
direct on line starter
    A kind of motor starter that does not reduce the voltage at the motor terminals.
direct torque control
    A method of estimating motor torque as part of a variable speed motor drive.
discrete cosine transform
    A mathematical technique for representing a sampled signal as a sum of cosine waves of different frequencies.
discrete Fourier transform
    A mathematical technique for representing a sampled signal as a sum of sine and cosine waves of different frequencies.
discrete-time signal
    A signal represented as a time series of samples taken at regular intervals.
displacement current
    The effect of a time-varying electric field, which induces a magnetic field just as the motion of electrical charges does.
display device
    Any device that displays data from an information system, such as a watch readout or an automatic scoreboard.
dissipation
    The loss of energy in a system, such as dielectric loss in a capacitor.
dissolved gas analysis
    A technique for fault detection in oil-filled transformers.
distributed control system
    A control system in which significant parts of the control process are decentralized.
distributed-element model
    An analysis of an electric circuit where capacitance, inductance, and resistance are distributed along the circuit, as in a transmission line, not concentrated in lumped components.
distributed generation
    An electrical grid where multiple small sources contribute energy, instead of relatively few large central generating stations.
distribution board
    A piece of electrical switchgear which distributes electric power to multiple branch circuits.
distribution transformer
    A power transformer, usually used to change the utility distribution voltage to a lower voltage for use on the customer premises.
Dolby
    A trademark for a noise reduction technique for analog sound recordings.
dot convention
    A system for marking terminals on instrument transformers to maintain correct polarity.
doubly fed electric machine
    An electric machine where both moving and stationary elements have external connections handling significant power.
downsampling
    A technique for reducing the number of signal samples processed by a digital system; decimation.
Dqo transformation
    A technique used to simplify mathematical analysis of polyphase electric circuits.
droop speed control
    A method of regulating generators so that multiple units share the load proportional to their ratings.
dual control theory
    A branch of control theory that deals with systems whose characteristics are initially unknown.
dual loop
    A method of supervising contacts and wiring in a security system, so as to detect some faults or tampering.
DVD
    Digital Versatile Disc, a type of optical disc for distributing video recordings and data using an orange/red laser.
dynamic braking
    A braking system that extracts energy from a moving system to bring it to rest; a dynamic braking system generally is not used to hold a position of a stationary object.
dynamic demand
    A technique for load management on an electrical grid based on frequency measurement.
dynamic programming
    A technique for optimization of the solution of a problem by combining solutions to smaller sub-problems.
dynamic random-access memory
    A type of semiconductor memory where data is stored as electric charges on capacitors; the charges must be refreshed periodically or else they will leak away, losing the stored data.
dynamo
    A direct-current generator, whose exciting field is provided by an electromagnet.

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E

Earth leakage circuit breaker
    A protective device that opens a circuit when stray voltage or current is detected that would present a hazard of electric shock.
eddy current
    An electric current induced inside a conductor exposed to a changing magnetic field.
edge detection
    An image processing technique used to identify boundaries of objects.
Edison effect
    The emission of an electric current from a hot wire; Edison did not realize he'd discovered the fundamental mechanism of the vacuum tube, thermionic emission.
electret
    A dielectric material that permanently retains an impressed electric field; the dual to a magnet.
electric arc
    Discharge of electric current through an open space between conductors; may be produced intentionally as a source of intense light and heat, or may be a result of an electrical fault.
electric charge
    The physical property of matter that causes it to experience a force when placed in an electromagnetic field.
electric circuit
    A closed path through which an electric current can flow.
electric current
    The motion of electric charges.
electric displacement field
    In Maxwell's equations, a vector field due to electric charges.
electric distribution systems
    That portion of an electrical grid that connects customers to substations or the bulk transmission system.
electric field gradient
    The rate of change of electric field with respect to distance.
electric field
    A vector field that exerts a force on electric charges.
electric generator
    A machine that converts mechanical energy to electrical energy by moving conductors through magnetic fields.
electric motor
    A machine that produces mechanical energy from electrical energy, by moving conductors through magnetic fields.
electric multiple unit
    Use of more than one electric locomotive on a train.
electric potential
    A measure of the work required to move a unit electric charge in an electric field.
electric power conversion
    Generally, changing the form of electric power.
electric power distribution
    In an electric grid, the network that brings power from a substation or bulk supply to individual customers.
Electric Power Research Institute
    A non-profit organization that carries out research on behalf of the US electric power industry.
electric power transmission
    The bulk movement of electric power for many customers from a generating plant to a local distribution network, usually at high voltage.
electric power
    The rate of transfer of electrical energy past a given point.
electric shock
    An injury caused to people or animals by electric current.
electrical cable
    A flexible conducting wire to carry electrical power or signals, usually covered with an insulating material.
electrical code
    A set of regulations for the use of electricity; they may vary from municipal to international in scope.
electrical conductivity
    A measure of a substance's ability to pass an electric current.
electrical conductor
    An object that carries an electric current, with little loss.
electrical contact
    A separable part of an electric device that carries current when touching another contact.
electrical discharge machining (EDM)
    Shaping of a work place by small sparks.
electrical element
    In circuit theory, a node at which some electrical property is concentrated (resistance, etc.).
electrical engineering
    The profession of applying electricity to practical problems.
electrical equipment
    Apparatus for generation, transmission or utilization of electric power.
electrical grid
    A geographically distributed system to connect source and users of electric power.
electrical impedance
    That property of a circuit that resists the passage of electric current, usually in the context of alternating current.
electrical insulation paper
    A grade of paper used for insulation of transformers, electrical machines, capacitors, and some cables.
electrical insulation
    A material that resists electrical current flow.
electrical load
    A consumer of electrical energy, turning it into light, heat, mechanical power, data, or chemical changes.
electrical machine
    Motors and generators, apparatus that converts between electrical power and mechanical power.
electrical measurements
    That branch of metrology concerned with electrical quantities.
electrical network
    A network of electrical components and conductors.
electrical polarity
    Identification of electrical terminals where current is flowing in the same direction relative to the device.
electrical steel
    Any of several types of steel used for manufacturing the magnetic field components of machines and transformers.
electrical substation
    A facility connecting a distribution network to a transmission network, usually with one or more transformers.
electrical technologist
    A specialist in applying electrical theory and technique to practical problems.
electrical wiring regulations
    The legal framework for electrical installations in buildings.
electrical wiring
    The installation of conductors, fixtures and protection devices for a structure or vehicle.
electricity meter
    An instrument to measure the electrical energy used by a customer for revenue purposes.
electricity pylon
    A structure, generally of wood or metal, to support wires.
electricity
    The set of physical phenomena associated with electric charges.
electrification
    Applying electric power to a process that was previously done by other means, or, development of an electric power system in a region that previously had none.
electroactive polymers
    A polymer that significantly changes size or shape when exposed to an electric field.
electrocardiograph
    A record of the electrical activity of the heart.
electrochemical engineering
    The profession of application of electrochemistry to practical problems.
electrodes
    An electrical contact that connects some medium to an electric circuit, such as in an electrochemical cell or a vacuum tube.
electro-diesel locomotive
    A railway locomotive with a diesel engine, generator, and electric driving motors that can be powered by the diesel engine or the track electrical supply.
electrodynamics
    The branch of physics that studies electrical charges and electrical currents.
electrolyte
    A liquid or solid medium that carries electric current in the form of ions.
electromagnet
    A magnet that generates a magnetic field from an electric current.
electromagnetic compatibility
    The control of unwanted electromagnetic interference.
electromagnetic field
    The field produced by moving electric charges and magnetic fields.
electromagnetic induction
    The production of current in a circuit by the change of magnetic field intersecting the circuit.
electromagnetic radiation
    Radio waves, light and other radiation that travels through space at the speed of light.
electromagnetic spectrum
    The range of frequencies of electromagnetic radiation.
electromagnetic wave equation
    A second-order partial differential equation that describes the propagation of electromagnetic waves through a medium or in a vacuum.
electromagnetism
    The science of electric fields, magnetic fields, currents, charges, and forces.
electromechanical
    A system that has both an electrical component and a mechanical component, such as a motor or a relay.
electromote
    An 1882 demonstration of a prototype electric trolley bus.
electromotive force
    A difference in electrical potential between two points, such as produced by a battery or a generator.
electron microscope
    An instrument that provides highly magnified images by use of an electron beam.
electronic amplifier
    A device that increases the power of an electrical signal by electronic means.
electronic circuit
    A circuit using one or more electronic devices.
electronic component
    An active or passive element of an electronic circuit.
electronic control unit
    In an automobile, an embedded electronic system that controls some aspect of a vehicle (ignition, transmission, and so on).
electronic design automation
    A system in which a computer provides assistance to the designer of a device or system.
electronic engineering
    The profession of applying electronics to practical problems.
electronic filter
    A filter that alters some frequency-related characteristic of a signal.
electronics
    The study of the flow of electrons through a vacuum, gases or semiconductors.
electronic speed control
    A device for regulating the speed of a motor.
electrophorus
    An instrument used to produce electrostatic charge through electrostatic induction.
electrostatic motor
    A motor that relies on the forces generated by electric fields, instead of magnetic fields.
electrostatics
    The study of stationary electric charges and resulting forces.
embedded operating system
    The common operating environment that supports embedded software; it may be a highly tailored version of a general-purpose operating system, or written solely for the purpose of embedded system operations.
embedded software
    A firmware component of a microprocessor-controlled system.
embedded system
    A computer system that controls a device or system, with no or a minimal user interface; for example, the ignition system in a car may have a microprocessor to control it.
enameled wire
    Wire insulated with a thin flexible layer of enamel, used for electrical windings.
energy demand management
    A system to adjust energy demand to reduce costs.
energy economics
    A branch of economics concerned with energy supply and demand.
energy efficient transformer
    A power transformer designed to have lower than average energy loss.
energy returned on energy invested
    A measure of how long an energy producing system takes to replace the energy it took to make it.
energy subsidies
    Payments to a consumer or producer of electric energy that are used as incentives for production or consumption.
engine-generator
    A combination of an internal combustion engine and a generator, often used as a standby power plant.
ENIAC
    The first general purpose electronic digital computer.
Epstein frame
    An apparatus used for testing of magnetic materials.
equalization (audio)
    Adjustment of the frequency response of a system to improve its utility.
equalization (communications)
    Adjustment of the frequency spectrum of a signal to cancel out the effect of the frequency response of a communication path.
equivalent circuit
    In circuit theory, a simple combination of elements that behaves at its terminals like a more complex combination.
equivalent impedance transforms
    A mathematical method to determine values of an equivalent circuit.
error correction and detection
    Techniques used to improve reliability of computer memory or communications channels by including extra information along with the desired data.
exponential stability
    A system that settles to a steady state after a disturbance, at a rate proportional to exponential time.
extended Kalman filter
    A strategy for estimating an unknown value in a non-linear system by combining multiple measurements.

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F

farad
    The SI unit of capacitance.
Faraday shield
    A solid conductive shield around a volume, which blocks electromagnetic fields.
Faraday–Lenz law
    One of Maxwell's equations, describing the relation between a changing magnetic field and production of an electromotive force.
Faraday's law of induction
    The relation between a changing magnetic field and the resulting voltage produced in a closed path.
fast Fourier transform
    A digital algorithm to analyze a time series of sampled data into a set of sine and cosine frequency components.
fault
    A short circuit, open circuit, or other disruption of a power system.
fax
    Facsimile, the transmission of paper images by radio or by wire.
feed forward
    A control system that adjusts the controlled variable based on a model of the process and measurements of disturbances, instead of feedback from measurement of the process.
feedback amplifier
    An amplifier that feeds back a small sample of its output to its input, to improve linearity.
feedback
    A system that samples part of its output and adds that to its input; feedback may be either positive or negative, aiding or opposing the initial input signal.
feed-in tariff
    A premium rate paid to distributed generators to encourage alternative energy sources.
ferrite core
    A magnetic core for an inductor made from a metal oxide compound.
ferroelectricity
    The property of materials that spontaneously maintain an electrical polarization, as a ferromagnetic material maintains magnetic polarization.
fiber optic cable
    A transmission medium that uses infrared energy or light to transmit information down a long thin transparent filament such as glass.
field effect transistor
    A transistor that relies on modulation of conductivity of a channel instead of injection of minority carriers as does a bipolar transistor.
field-oriented control
    A control strategy for variable frequency drives that models the magnetic field of the motor to control its torque.
filter
    A circuit that selectively alters a signal based on its frequency components.
filter capacitor
    In a power supply, a capacitor that smooths the DC voltage produced by a rectifier stage.
finite impulse response
    A class of digital filters whose response to an impulse returns to zero in finite time.
firmware
    Software of a computer that is never or rarely altered during its working life, for example, the control computer program for an automotive ignition system.
Fleming valve
    The first important vacuum tube device, used as a radio detector.
Fleming's left-hand rule for motors
    A mnemonic to recall the relative orientation of current, magnetic field and resulting force for electric motors.
Fleming's right-hand rule for generators
    A mnemonic to recall the relative orientation of current, magnetic field and resulting force for electric generators.
fluorescent lamp
    A type of electric lamp that relies on a phosphor coating to produce visible light from the ultraviolet light generated by a mercury discharge.
flux linkage
    In a magnetic system, that part of the magnetic flux that passes through a given closed path, which may be a winding.
flyback converter
    A type of voltage converter that stores energy in an inductor.
flyback transformer
    A type of transformer that recovers energy stored in its own core. Historically used in the deflection circuits of CRT display systems.
forward converter
    A type of voltage converter that relies on transformer action to couple energy to its output circuit.
fossil-fuel phase-out
    A plan to replace coal, oil, or natural gas fuel with other sources to produce electrical energy.
fossil-fuel power station
    A power plant using coal, oil, or natural gas fuel.
Fourier series
    A set of coefficients of sine and cosine waves; this can represent a time function as a function of frequency.
Fourier transform
    An algorithm for converting a continuous waveform in the time domain into an equivalent set of spectral components in the frequency domain.
free space optical communications
    Transfer of information from point to point by a beam of light or infrared energy, instead of a wired connection or radio waves.
frequency changer
    An electric machine used to transfer power between two networks with different frequencies, or, an electronic device (more usually called a frequency mixer) that changes the frequency of an input signal to some other frequency.
frequency modulation
    A method of impressing information on a carrier wave by changing its frequency.
frequency response
    The measure of the output of a system in response to an input of varying frequency.
full load current
    The current drawn by a motor or other electrical machine at its full rated power and standard voltage.
full-wave rectifier
    A rectifier circuit that converts both positive and negative parts of the input alternating current waveform into a unidirectional, direct current.
fuse
    A circuit protective device that interrupts excessive current by melting a metal strip.
fuzzy control
    A control system that relies on fuzzy logic instead of binary true/false conditions.

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G

gain scheduling
    A technique for control of non-linear systems that use different control parameters based on some measurement of the process controlled.
galvanic corrosion
    Electrochemical corrosion of one metal in contact with another.
galvanometer
    An instrument for detecting small electric currents.
gamma ray
    Electromagnetic radiation with wavelengths shorter than ten nanometres. Strictly: radiation that is produced in the nucleus of atoms.
gas-filled tube
    An electron tube device that relies on the presence of gas for operation, usually at less than atmospheric pressure.
gate turn-off thyristor (GTO)
    A four-layer power semiconductor device that can be turned on and off by signals at a control (gate) terminal.
Gauss's law
    A mathematical relation between the electric flux passing through a surface and the charge contained within that surface.
generator
    In circuit theory, an ideal voltage source or an ideal current source, whose properties are independent of the connected circuit.
governor
    A speed regulator for a machine such as a steam engine; an early important feedback control cybernetic system.
grid energy storage
    Any system tied to an electrical grid that stores electrical energy at low demand times and releases it to meet peak loads; it might be a centralized station like a pumped-storage hydroelectric plant, or might be distributed over many customer sites such as by the use of electric vehicle batteries.
grid-tie inverter
    A power inverter that allows synchronization with the electrical grid for export of energy surplus to the facility's needs.
ground
    A reference point for electrical potential; often connected to the Earth.
ground and neutral
    Protective and circuit return conductors in a wiring system.
ground-level power supply
    A system for providing powers for electric trams without overhead wires and without a permanently energized third rail.
growler
    A test instrument that is used to diagnose some faults with AC motors.
GSM
    The second generation of cellular mobile phone technology, deployed since 1991 in Europe.
Gunn diode
    A two-terminal solid-state device that is used in microwave oscillators.
gyrotron
    A high-power vacuum tube oscillator that can produce microwave frequencies up to hundreds of gigahertz at power levels up to megawatts.

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H

H infinity
    An optimization strategy for certain classes of control problems.
Hall effect sensor
    A device that detects and measures magnetic field by the Hall effect voltage induced in a current-carrying semiconductor.
harmonic distortion
    An effect of a non-linear signal path that introduces frequencies that are integer multiples of an input frequency.
harmonic oscillator
    An oscillator which produces sinusoidal output, such as a simple RLC oscillator.
harmonic
    A waveform that has a frequency which is an integer multiple of another frequency.
harmonics
    Distortion of the power line voltage due to non-linear loads such as rectifiers.
H-bridge
    An array of four controlled switches that coverts direct current to alternating current, with peak value equal to the supply voltage.
HDTV
    High Definition Television, any television system with more than 625 scan lines.
headphone
    An audio transducer or pair of transducers arranged to be worn on (or in) the ear.
heat transfer
    The study of the flow of heat energy; heat transfer concerns dictate major design features of most electrical and electronic systems.
heatsink
    A structure intended to dissipate heat from an active device into the ambient environment.
Heaviside step function
    A mathematical unit step function useful in the solution of certain differential equations by the methods of operational calculus.
Helmholtz coil
    An arrangement of coils useful for producing a uniform magnetic field within a certain volume.
henry
    The SI unit of inductance.
Hertz
    The SI unit of frequency, equivalent to one cycle per second.
heterodyne
    The process of mixing signals of a number of frequencies to produce new frequencies.
heterostructure
    A semiconductor device built of two or more dissimilar materials.
Hi-Fi
    High Fidelity, the set of techniques for reproduction of sounds that appear natural in source.
high-voltage cable
    A flexible insulated electrical conductor designed to withstand a significant voltage; "high" voltage may be hundreds or hundreds of thousands of volts, depending on the context.
high voltage
    Any voltage at which safety concerns apply; in some contexts, anything over 100 volts may be a high voltage; in electric power transmission, voltages over 66,000 volts are considered "high voltage".
high-pass filter
    An electrical network that tends to pass higher frequencies and block lower ones.
high-voltage direct current
    A system for power transmission that uses high DC voltages for reasons of economy or stability.
high-voltage switchgear
    Electrical apparatus designed for control of high-voltage circuits.
Hilbert transform
    A mathematical operation used in signal processing.
holography
    The technique of representing the image of a scene by a recording of interference patterns of the light field.
home appliance
    Any electrical appliance intended for use in a home.
homopolar generator
    A generator in which current and magnetic field direction are constant as the machine rotor revolves.
homopolar motor
    A motor that produces torque from a current and magnetic field that does not change direction.
horsepower
    A unit of power, equivalent to around 746 watts.
hot wire barretter
    A current dependent resistor formed of a fine wire in an envelope, useful for regulating current.
humidistat
    A switch that operates automatically on detecting a change in moisture content of the air.
HVAC
    High Voltage Alternating Current; depending on context, this could be hundreds or hundreds of thousands of volts.
HVDC converter station
    An element of a high-voltage direct current power transmission system; each end of the transmission line has a converter station connected to the local AC grid.
HVDC
    High Voltage Direct Current.
hybrid coil
    A kind of transformer used for bidirectional transmission of signals over one pair of wires, for example, as in an analog telephone set.
hydroelectricity
    The generation of electric power from the kinetic energy of falling water.
hydropower
    Power (now nearly always electric power) generated from falling water; hydroelectricity.
hysteresis
    A characteristic of a system where its state is history-dependent.

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I

IGBT
    Insulated Gate Bipolar Transistor, a power semiconductor device that combines some of the advantages of field-effect and bipolar transistors.
image impedance
    A parameter used in design of electrical networks such as filters.
image noise reduction
    Any technique used to reduce interfering effects in processing of an image.
image processing
    Electronic recording, storage, alteration and reproduction of pictures.
impulse response
    The response of a network to a sudden narrow pulse input.
incandescent light bulb
    A device that uses a fine wire filament heated by an electric current to make light...and heat.
induction coil
    An early name for a transformer; a type of transformer for high-voltage uses.
induction cooker
    A cooking appliance that heats pots with magnetic fields.
induction generator
    A type of generator where the rotating field winding is excited by induction from the stationary armature winding.
induction motor
    A type of motor where the rotating field winding is excited by induction from the stationary armature winding.
induction regulator
    A kind of variable transformer that provides stepless control of the output by changing the coupling between two coils.
inductive coupling
    Transfer of energy between two circuits through the magnetic field that passes through both.
inductive output tube
    A high power, high frequency amplifier tube, in some forms capable of megawatt pulses at hundreds of megahertz.
inductor
    A circuit component with a concentrated inductance; a coil; stores energy in a magnetic field.
industrial and multiphase power plugs and sockets
    Electrical fittings used to connect cables to three-phase power circuits.
industrial automation
    The general practice of automatic control applied to industrial operations.
infinite impulse response
    A filter which, mathematically, never gets to a zero effect of an impulse at its input, though practically the response may become negligible after a definite time.
information appliance
    Conceptually, an embedded computer system with a specialized user interface designed to simplify one task, such as e-mail or photos; a modern smart phone approaches this concept.
information theory
    The mathematical study of information.
information
    In one sense, the answers to uncertainties.
input/output (I/O)
    That part of a computer system devoted to exporting and importing data, for example, in human-readable form.
inrush current
    The transient current that flows when first connecting a device to a power source.
Institute of Electrical and Electronics Engineers (IEEE)
    The American-based society for electrotechnology.
Institution of Engineering and Technology
    The British society of electrical and electronics engineers.
instrumentation engineering
    The profession dealing with development of measuring systems.
instrumentation
    A device that turns some physical property into a measurement.
insulation monitoring device
    A supervisory device to detect failure of electrical insulation.
insulator
    A substance that does not permit easy flow of electric current; a fitting intended to support a conductor.
integrated circuit
    An interconnected array of electronic devices, factory assembled on a single substrate.
intelligent control
    The application of artificial intelligence techniques to process control.
intelligent transportation system
    The application of information technology to manage some aspects of a transportation system.
intermittent energy source
    An energy source whose availability is not under human control; it may be sporadically available or available on some natural schedule not coincident with human demands; energy sources that are not dispatchable.
International Electrotechnical Commission (IEC)
    An international standards organization devoted to electrical standards; most countries are members.
International Organization for Standardization
    An international organization coordinating the efforts of national technical standards organizations.
interrupter
    Any of a series of automatically operated electromechanical switches that periodically opened and closed a circuit.
inverter
    A system that converts direct current power to alternating current, without the use of rotating machines, using electron devices such as mercury arc valves or thyristors.
iron loss
    That portion of the wasted power of a machine or transformer attributed to hysteresis and eddy currents in the iron core.
isolated-phase bus
    A bus where each phase is in its own grounded metal enclosure to prevent faults from spreading from phase to phase; often used in large power plant generators.
isolation transformer
    A transformer especially intended to prevent leakage current from passing from its primary circuit to the secondary circuit.
iterative learning control
    A technique for improving the accuracy of control systems that carry out the same sequence repeatedly.

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J

j operator
    Electrical engineering uses "j" to represent the imaginary unit "i", to prevent confusion with the symbol for current. j × j = − 1 {\displaystyle j\times j=-1} {\displaystyle j\times j=-1}.
Jedlik's dynamo
    An early form of electric generator using electromagnets.
JFET
    A field effect transistor with a reverse-biased PN junction between gate and channel.
jitter
    Deviation from the true periodicity of a periodic signal.
Joule heating
    Heating in a conductor due to passage of current.
joule
    The SI unit of work; one joule is of the order of the energy dissipated when an apple falls off a table top.

K

Kalman filter
    An algorithm for estimating an unknown value from a series of approximate measurements.
Kelvin–Stokes theorem
    A theorem in calculus, useful in analytic solutions of problems in electromagnetism.
Kilovolt-ampere
    A unit of apparent power.
Kirchhoff's circuit laws
    The observation that the sum of the currents at any node of a circuit must be zero, and the sum of the voltage differences around any loop must be zero; often abbreviated "KCL" and "KVL" in lecture notes.
Klystron
    A type of microwave oscillator vacuum tube.

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L

LAN
    Local Area Network, an interconnection of computers over a building or small campus.
Laplace transform
    A mathematical operation for solution of differential equations by transforming them to the s domain from the time domain.
laser diode
    A semiconductor device that produces coherent laser radiation when properly energized.
leakage inductance
    The inductance of a transformer that results from magnetic flux not linked by both primary and secondary windings.
light-emitting diode
    A semiconductor device that produces light or infrared or ultraviolet radiation when properly energized.
linear alternator
    An electrical machine that generates electric power from the relative straight-line motion of its parts.
linear motor
    An electrical machine that generates electric force in a straight line by the interaction of its moving parts and magnetic fields.
linear variable differential transformer
    A transducer that produces an electrical signal proportional to the movement between its parts.
lineman
    A specialist technician who installs outside plant wiring (overhead circuits, power transmission lines).
Litz wire
    A kind of stranded wire used to minimize losses in coils.
load flow study
    A mathematical prediction of the flow of electric power in a network, based on a model of the actual or proposed system; necessary for planning of electrical grids.
load following power plant
    A power plant that can economically be operated over a significant range of output, so as to meet varying electric power demand.
load-loss factor
    A factor for estimating energy lost in a distribution network due to load current.
load management
    Any strategy for altering the operation of customer loads so as to reduce peak demand on an electrical grid.
load profile
    The daily, weekly, or annual plot of electrical load against time.
local positioning system
    A navigation system that doesn't cover the whole Earth; such as over a continent, or even within a building.
LORAN
    A radio navigation system developed from a World War II military system (GEE), used for civilian purposes till the 1980s.
Lorentz force law
    The mathematical relation between currents in conductors and the resulting magnetic forces between them.
lossless data compression
    Any data compression method where the source can be reconstructed exactly; where approximations are tolerable, lossy data compression can be used.
lossy data compression
    Any data compression method which allows only a close approximation of the source to be reconstructed; useful for images or music, where the human perceptual system compensates for the errors.
loudspeaker
    A transducer that converts electrical current into sound, perceptible to more than one listener.
low-noise amplifier
    In a satellite radio receiving system, an amplifier placed near the antenna.
low-noise block downconverter
    In a satellite radio receiving system, a device that amplifies and converts signals to a lower frequency band that will have lower losses in interconnecting cables.
low-pass filter
    An electric filter network that passes lower frequencies and blocks higher ones.
LTI system theory
    The theory of systems that, over a useful range, respond proportionally to inputs and don't change characteristics while responding.
lumen
    The SI unit of luminous flux, the energy of visible light.
lumped parameters
    Describes an electrical network where the circuit elements are small compared to the wavelengths of the signals passing through it.
Lyapunov stability
    A criterion for stability of a dynamical system; if disturbances from a stable point reduce and the system returns to that stable point, it can be said to be Lyapunov stable.

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M

machine learning
    The set of artificial intelligence techniques for systems that can follow examples to solve new problems.
magnet wire
    The class of wire manufactured for winding electromagnetic coils such as in motors or transformers.
magnetic blowout
    A component of a switching device that uses a magnetic field to assist in extinguishing the arc, using a permanent magnet or a coil.
magnetic circuit
    A path through which magnetic flux passes.
magnetic constant
    The constant that relates the strength of magnetic flux to magnetic induction in free space.
magnetic core memory
    A type of computer memory that stores data as magnetization in tiny rings of ferrite material.
magnetic field
    A field that causes magnets and currents to experience forces.
magnetic flux density
    The amount of magnetic field per unit area; in SI units, measured in webers per square metre.
magnetic flux
    The magnetic field; a conductor that encloses a changing magnetic flux will have a voltage induced in it.
magnetic moment
    The proportionality constant that relates the twisting torque produced on an object to the magnetic field.
magnetism
    The class of natural phenomena related to magnets and magnetic fields.
magnetization
    A property of a material that measures its response to a magnetic field.
magnetization current
    In a transformer, that portion of the current used to support magnetic flux.
magnetostatics
    The study of stationary magnetic fields.
magnetostriction
    A property of some materials that change shape when subject to a magnetic field.
magnifying transmitter
    A concept for a signal transmitter that used a resonant transformer to provide a high voltage.
main distribution frame
    In a telephone central office, the equipment that connects to subscriber circuits.
mainframe computer
    A large centralized computer system, used for large volumes of data or supporting multiple interactive terminals, with large input/output capacity, generally expected to provide critical services to a business or institution with a predictable degree of reliability.
mains electricity
    Commercial electric power, purchased from an off-site source shared by many consumers. Regional supplies vary in voltage, frequency, and technical standards.
mains hum
    Interference on an audio or visual signal related to the power line frequency.
marginal stability
    Said of a system that neither returns to its initial state when disturbed nor diverges to some unstable condition.
marine energy
    Any technique for extracting useful energy from tides, waves, or salinity or temperature gradients of the ocean.
Marx generator
    A kind of circuit for generating very high DC voltage pulses.
Maser
    A device that produces microwave energy in a similar manner to a LASER.
maximum prospective short-circuit current
    The calculated value of current that could flow if a short circuit occurred; a parameter for selection of circuit protection devices.
Maxwell's equations
    The fundamental relations between electric and magnetic fields, expressed in concise mathematical form.
mechanical rectifier
    An electromechanical device for converting alternating current to direct current, using sets of contacts which operate in synchronism with the AC.
mechatronics
    Combinations of mechanical systems with electronics for sensing and control.
memristor
    A hypothetical non-linear passive two-terminal electrical component relating electric charge and magnetic flux linkage.
mercury-arc rectifier
    A mercury-arc valve; a vacuum tube device that converts alternating current to direct current by an arc in mercury vapor; displaced by solid-state devices, but formerly much used especially in high-voltage direct current transmission.
mercury vapor lamp
    A lamp that generates light from a discharge struck in mercury vapor; formerly widely used in outdoor lighting, now replaced by lamps with better efficacy.
mesh analysis
    A strategy for solution of the voltage distribution in some types of electrical networks.
mesh networking
    A topology where infrastructure nodes connect to other nodes such as to convey information.
Metadyne
    A DC electric machine with crossed fields and two sets of brushes, used as an amplifier or rotary DC transformer.
metal rectifier
    A rectifier made from copper oxide or selenium; formerly widely used before development of silicon rectifiers.
micro combined heat and power
    Equipment that generates process or space heat and electric power, of a size useful for a single building.
microcontroller
    A microprocessor integrated with memory and input/output circuits, useful for embedded control.
microelectromechanical systems
    An electromechanical system of microscopic size; they may be sensors or actuators.
microelectronics
    That part of the field of electronics dealing with integrated circuits.
microgeneration
    Small-scale electric power production, to provide the needs of a small building or individual consumer.
microphone
    A transducer that changes sound into electrical signals.
microprocessor
    A computer with its logical, arithmetic and control functions implemented on one or a few integrated circuits.
microstrip
    A planar transmission line that is fabricated by printed circuit board technology and is used for microwave-frequency signals
microstrip antenna
    A planar antenna that is fabricated by printed circuit board technology
microwave oven
    A heating appliance that uses microwave energy.
microwave radio
    The subset of radio technique using wavelengths that are in the range of 3 GHz or higher.
microwave
    Part of the radio spectrum with wavelengths shorter than 10 centimetres.
Millman's theorem
    A theorem stating the relation between branch currents and voltages for multiple sources in parallel.
mineral-insulated copper-clad cable
    Cable with an outer metal cover and insulated by powdered inorganic material, suitable for high temperature; one kind of fire-resistant cable.
mobile phone
    A handset that connects to the public switched telephone network by radio.
Modbus
    A brand name for a serial protocol for industrial control equipment communication.
model predictive control
    A control strategy for process systems based on a mathematical model of the process and its disturbances.
modem
    Modulator-Demodulator, an interface between a computer system and a telephone network.
modulation transformer
    Part of a radio transmitter used to impress modulation on one amplifying stage.
modulation
    The impression of information on a carrier wave for transmission.
monolithic microwave integrated circuit
    An integrated circuit that operates in microwave frequencies and that can be fabricated by printed circuit board technology.
monoscope
    A raster scan video device that generates a single fixed image for test or identification purposes.
Moore's law
    The observation that the number of transistors possible in an integrated circuit doubles approximately every two years.
Morse code
    A method of transmitting text by long and short impulses and varying delays between them.
MOSFET
    Metal Oxide Semiconductor Field Effect Transistor, a class of transistor using a single type of charge carrier and with a very thin insulating layer between current channel and control gate. If you count those built into integrated circuits, nearly all transistors are MOSFETs.
motion control
    That part of automation that deals with accurately controlling the movements of machines.
motor controller
    Electrical apparatus that regulates and protects an electric motor, which may be as simple as an on-off switch or a servo system for precision machine tools.
motor soft starter
    A device that reduces the inrush current when an electric motor is first connected to the power supply.
MP3
    A standard for encoding audio in digital form.
MRI
    Magnetic Resonance Imaging, a technique for examining the interiors of, for example, medical patients, using sensitive measurements of the magnetic fields of atomic nuclei.
multics
    An influential early time-sharing computer operating system, first released in 1969.
multimeter
    A test instrument that can measure current, voltage, or resistance (though not concurrently).
Multisim
    A brand of computer software for electronic circuit simulation.

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N

nameplate capacity
    The design power output of a generator, at specified temperature rise.
nanoinverter
    Grid tied inverters rated less than 100 watts, useful for connection of single solar PV panels to a building AC power system.
nanotechnology
    Technology that uses devices whose principal dimensions are of the order of a few nanometres.
National Electric Code
    The United States national technical standard for building wiring installation.
National Electrical Manufacturers Association (NEMA)
    A US trade association for electrical manufacturers that also develops technical standards.
negative feedback
    Feedback from a control system output that tends to oppose the input.
negative resistance
    A voltage/current characteristic where increasing current leads to decreased voltage drop across the device.
negawatt power
    In power grid demand management, that portion of load that can be met by conservation efforts or improved energy efficiency.
neon sign
    Strictly, a sign that glows orange because of a discharge through neon gas; less pedantically, any gas discharge tube formed into a sign.
neon-sign transformer
    A high-voltage transformer with features intended to support operation of a neon sign.
net metering
    A metering plan that allows grid customers with their own generation to be billed only for their net import of energy from the grid.
network analyzer
    An analog computer system for modelling power grids; displaced now by digital computers.
network cable
    Cables intended for use in data interconnections, with defined performance parameters.
network protector
    A type of circuit breaker used to isolate a fault from a multi-transformer supply network.
neural networks
    A network of individual logic elements in multiple layers that emulates some of the behavior of a biological nervous system; a technique in artificial intelligence.
nodal analysis
    A technique for analysis of currents in an electrical network.
node
    A defined point in an electrical network, with some potential relative to a reference node and where currents can be summed.
noise cancelling
    A type of microphone that preferentially picks up a nearby sound source and rejects ambient noise.
noise reduction
    The techniques used to reduce the perception of noise in a communications path.
noisy-channel coding theorem
    A theorem that establishes the limits of the error-free data transmission in a noisy communication channel
nominal impedance
    The rated impedance of an element of a circuit.
nonlinear control
    The class of control problems relating to the control of systems that are nonlinear.
nonode
    Any electron device (although practically, only vacuum tubes) with nine internal active electrodes controlling electron flow.
Norton's theorem
    A theorem which states that any network of current sources, voltage sources, and resistors can be simplified to an equivalent network with only a current source and shunt admittance; the dual of Thevenin's theorem.
notch filter
    A filter with a narrow reject band, used to block, for example, a pilot tone out of a communications network.
NTSC
    The US National Television Systems Committee, that developed the analog monochrome and color television standards used for more than 60 years for broadcasting.
nuclear power
    Production of electric power (or propulsion power) by nuclear fission or fusion.
numerical control
    Digital automatic control, especially of machine tools.
Nuvistor
    A type of miniature vacuum tube, developed around the same time transistors became common in consumer electronics.
Nyquist frequency
    The maximum frequency that a sampling system can represent accurately.
Nyquist stability criterion
    A graphical technique for evaluating stability of a feedback system.
Nyquist–Shannon sampling theorem
    A theorem that establishes the necessary rate to accurately sample a band-limited signal.

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O

observability
    In control theory, the measure of how well the internal state of a system corresponds to its measurable outputs.
Oersted
    The CGS unit of magnetic field H.
ohm
    The SI unit of electrical resistance.
ohmmeter
    An instrument that measures electrical resistance.
Ohm's law
    The mathematical relationship between voltage, current, and resistance.
one-line diagram
    A simplified schematic diagram of a power system.
on-premises wiring
    Telecommunications wiring owned by the customer.
open-circuit test
    A test, of a transformer or other device, with no load connected.
open-circuit voltage
    The voltage developed at the terminals of a device with no load connected.
open-circuit time constant method
    A method for approximately evaluating the transfer function of an electrical network.
operational amplifier
    A type of amplifier with differential inputs, widely used in circuits where feedback determines the circuit properties.
optical fiber
    A glass or plastic fiber used to convey signals transmitted by visible light or infrared radiation.
optimal control
    The branch of control theory studying optimization of a control system to fit some optimization criterion.
oscillation
    A periodic cyclical motion or disturbance.
oscilloscope
    An instrument for graphically displaying a waveform as a function of time.
Oudin coil
    An early form of high-voltage induction coil identical in principle to a Tesla coil except for being constructed essentially as an auto-transformer.
out of phase
    The condition when AC generation sources are not synchronized.
overhead line
    Outside plant run on poles or other structures; power transmission or telecommunication wires.
oversampling
    Sampling a signal at a rate higher than required by the Nyquist criterion.
overshoot
    A transient excursion of a signal beyond its stead state value.
overvoltage
    Application of more than rated voltage to a device.
oxygen-free copper
    A grade of copper preferred for electrical applications for its low electrical resistance.

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P

padmount transformer
    A kind of metal enclosed distribution transformer suitable for mounting on grade.
pantograph
    A linkage that supports the current collector of an electric locomotive.
paraformer
    A device similar to a transformer that couples energy between two circuits by varying magnetic parameters.
parameter estimation
    In estimation theory, the practice of assigning values to a process model so it accurately predicts the process's behavior.
Park transform
    A mathematical technique useful in the analysis of three-phase systems.
partial discharge
    Breakdown of insulating gas or solid material by an electric field, but without formation of an arc.
passivity
    Incapable of adding energy to a signal or process.
patch cables
    Short cables with connectors, used to make connections between outlets of a patch panel or for temporary connections to a system under test.
peak demand
    The maximum rate at which energy is consumed from an electrical grid; may be either an instantaneous measure or the maximum energy transferred in some interval such as 15 minutes.
Peltier–Seebeck effect
    The thermoelectric effect, movement of heat due to electric current flow.
pentagrid converter
    A type of self-oscillating vacuum tube used a frequency mixer in superheterodyne receivers.
pentode
    Any five-electrode electron device, but usually a kind of vacuum tube.
permanent magnet synchronous generator
    An AC generator that uses a permanent field magnet instead of an electromagnet.
permanent magnet
    A magnet that retains its polarization after an external field is removed.
permeability
    The amount of magnetisation in a material resulting from an applied magnetic field.
phase converter
    Electrical apparatus that converts power from a system of phases to another system, for example, converting single-phase power to three-phase.
phase-fired controllers
    An AC power controller that adjusts the effective value of output by switching on at a variable time phase in the AC cycle.
phase locked loop
    An oscillator circuit that produces an output signal that is in a fixed timing relation to a reference input.
phase modulation
    Impressing information on a carrier wave by advancing or delaying the waveform slightly; related to frequency modulation.
phasor
    A vector representing a signal of a given frequency in phase space.
phasor measurement unit
    A system that measures the timing and amplitude of voltages and currents on an electrical grid, synchronized over a wide geographic area; the resulting measurements can be used to manage power flow on the grid.
phonograph
    A record player, a device that converts the mechanical movements of a stylus in a disk or cylinder recording groove into sound.
photocell
    A light sensor that produces or alters a voltage when light is present.
photodetector
    Any device that detects visible light.
photodiode
    A two-terminal device whose terminal voltage or current changes in response to light.
photometer
    An instrument that measures light.
photonics
    The technology of conveying information through light or infrared radiation.
photoresistor
    A resistor whose resistance varies when light strikes it.
phototransistor
    A transistor sensitive to light.
PID controller
    A process control system that has proportional, integral and derivative terms in its response to errors between measured value and setpoint.
piezoelectric effect
    Production of a voltage in response to mechanical pressure or mechanical deformation.
piezoelectric motor
    A type of motor that uses piezoelectric elements to generate force.
PIN diode
    A multilayer semiconductor diode with a thin region of intrinsic material between its p-doped and n-doped regions.
planar graph
    In network theory, a set of nodes and interconnecting lines that can be given in one plane without crossing lines.
plasma
    A state of matter where electric charges are free to move.
plenum cable
    A fire-resistant data communications cable that is permitted to be installed in the air handling spaces of a modern building.
plug-in hybrid
    A hybrid electric vehicle that can be recharged from grid power as well as its own engine/generator.
P-N junction
    The boundary between two differently doped regions of a semiconductor.
polarization density
    A measure of the increase of the intensity of an electric field over that in free space, owing to the separation of atomic-scale electric dipoles.
polyphase coil
    A coil intended for connection to a polyphase power supply.
polyphase system
    An alternating current power transmission system using three or more wires, each of which carries a current that is displaced in time with respect to the others.
Pontryagin's minimum principle
    A mathematical principle used in the theory of optimal control.
port
    Any place at which energy can be observed to enter or leave a system.
positive feedback
    Feedback from the output of a system that tends to increase the effect of any input; if overdone, leads to instability.
potential difference
    A voltage difference, the amount of work required to bring a test charge from one point to another divided by charge magnitude.
potentiometer
    A three-terminal variable resistor, which can be configured as an adjustable voltage divider.
power BJT
    A bipolar junction transistor that can be used in circuits handling a watt or more of power.
power cable
    Flexible insulated electrical conductors used to transmit electric power.
power conditioner
    Any system intended to alter some property of the bulk power supply to improve it for some application; such as filters, surge suppressors, voltage regulators, uninterruptible power supplies, and many others.
power consumption
    The rate at which a device consumes energy.
power converter
    Apparatus intended to convert electric power to another form of electric power, such as conversion between AC and DC or changing frequency or phase number.
power distribution
    That portion of an electrical grid between the substation or bulk supply and the end consumer.
power electronics
    The class of electronic devices handling power greater than a watt.
power engineering
    That part of electrical engineering that deals with the generation, distribution and consumption of electrical power.
power-factor correction
    Apparatus intended to bring the power factor of some load closer to 1.
power factor
    The ratio of apparent power flowing to a load divided by the real power.
power-flow study
    A load flow study; mathematical prediction of the magnitudes and direction of power flow in an existing or planned power grid; an essential part of grid management.
power generation
    The practice of converting other energy sources to electric power.
power grid
    An interconnected network of generators, transmission lines, and apparatus for reliable and economic transmission and utilization of electric power.
power inverter
    A DC to AC power converter.
power-line communication
    The impression of carrier waves on a power line circuit for signalling purposes.
power MOSFET
    A metal oxide semiconductor field effect transistor suitable for use in circuits handling more than a watt of power.
power plant
    A facility that converts other energy forms into electric power.
power rating
    The nominal power that an apparatus or machine can handle, with specified or customary temperature rise and life expectancy.
power quality
    Conformance of an electrical power supply with its specifications.
power storage
    A facility that changes electric power into some form that can be stored and usefully reconverted back to electric power, for example, pumped storage or battery systems.
power supply
    A subsystem of a computer or other electronic device that turns electric power from a wall plug or batteries into a form suitable for use by the system.
power-system automation
    The implementation of power-operated switching and control that allows automatic operation of power system elements, instead of manual operation.
power-system protection
    The technology of limiting the spread of failures of a power system to a minimum, and of preventing permanent damage to apparatus or conductors by such faults.
printed circuit board
    An etched wiring assembly for interconnection of electronic components.
printer
    A device that makes permanent human readable images and text from computer data.
process control
    The field of study of automatic control of processes.
programmable logic controller
    A computer system designed to be rugged enough for industrial use and with a programming environment highly tuned to the domain of industrial control problems.
programming language
    A formalism for human-readable instructions to a computer.
protective relay
    An electromechanical or electronic device that detects faults on a power system and can signal circuit breakers to operate.
proximity effect
    The increase in circuit resistance when the magnetic fields of multiple AC currents interact.
pulse transformer
    A transformer designed to create or transmit pulses.
pulse-width modulation
    Transmission of information by varying the duration of pulses, or, varying the average output voltage of a power converter by varying the duration of pulses.
pulse-amplitude modulation (PAM)
    Transmission of information by varying the magnitude of a stream of pulses of fixed frequency.
pulse-code modulation
    Any system for conveying analog information by altering some property of a stream of pulses.
pumped-storage hydroelectricity
    A grid energy storage system that pumps water uphill for later use by a hydroelectric generator plant.
push switch
    A device that closes or opens an electrical circuit when pushed.
push–pull converter
    A converter with two sets of primary switching elements so that the transformer primary voltage can be reversed on each cycle.

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Q

quadrature booster
    A phase shifting transformer that can inject voltages that are time delayed with respect to the input voltage.
quality factor
    In a resonant circuit, the ratio of stored energy to energy dissipated on each cycle of oscillation.
quantization
    Analog to digital conversion, changing a continuously varying analog signal to discrete digital numbers.

R

radar cross section
    The effective reflecting area of a radar target, which varies with frequency, geometry, and surface composition.
radar
    Radio Detection and Ranging, the techniques for observing the speed and position of objects by reflected radio waves.
radio frequency
    Electromagnetic waves with frequencies less than that of infrared radiation; commercially important radio frequencies range from tens of kilohertz up to around a terahertz.
radio transmitter
    Apparatus designed to generate radio frequency electric current, which, connected to an antenna, can radiate energy through space.
radio
    The technology of radio frequency devices.
railway electrification system
    A set of standardized methods for applying electric power in railway traction.
Rankine cycle
    A thermodynamic cycle, an idealized version of the operation cycle of a steam turbine.
reactive power
    That component of apparent power flow due to the return to the source of energy stored in a load's electric or magnetic fields, that does no useful work at the load.
real-time operating system
    A computer operating system that ensures responses with a bounded time to events such as in a controlled process.
receiver
    The apparatus that takes radio-frequency currents induced in an antenna and turns them into useful signals.
rechargeable battery
    A secondary battery; a battery that can have a useful portion of its capacity restored by connection to a supply of electric current.
reciprocity (electrical networks)
    A theorem that states that the current injected into one point in a network will produce a voltage at a second point that is identical to the voltage produced at the first point by injection of the same current at the first point
reciprocity (electromagnetism)
    An observation that electric currents and electric fields can be analyzed from either point of view as regards the source of the energy in the system; for example, in radio, a good transmitting antenna is generally also a good receiving antenna.
record player
    A phonograph; a device that turns the variations in a disk or cylinder recording groove into sound.
rectifier
    A device that converts alternating current (which periodically reverses) to direct current that flows in only one direction; may be a solid-state, vacuum tube or electromechanical device.
rectiformer
    A combination of a transformer and a rectifier, used in electrochemical processes or supply of electrostatic precipitators.
recursive least squares filter
    An algorithm for a digital filter system.
Reed switch
    An electrical switch made of two thin strips of ferromagnetic metal, which touch when subject to a magnetic field.
regenerative braking
    A braking scheme that returns energy to the source.
regenerative circuit
    A circuit that employs positive feedback; can be an amplifier or an oscillator.
relaxation oscillator
    An oscillator that relies on an active device periodically changing state; such oscillators usually produce a square-wave or sawtooth waveform, different from the approximately sinusoidal waveshape of a harmonic oscillator.
relay
    An electrically operated switch.
reluctance motor
    A type of electric motor that induces non-permanent magnetic poles on the ferromagnetic rotor, relying on varying magnetic reluctance; the rotor carries no windings.
remanence
    That portion of the applied magnetic field that the material retains when the external field is removed.
remote racking system
    A system for inserting circuit breakers into switchgear that allows the operator to stay at a safe distance from any possible arc hazard.
remote sensing
    Acquisition of measurements of an object without contact, for example, measuring soil moisture by radar from an aircraft.
renewable electricity
    Electric power derived from primary energy sources that replenish on a rapid scale or that are not appreciably diminished by human exploitation.
renewable energy payments
    Any incentive program to improve the economic return of a renewable energy project.
renewable energy policy
    Government plans to displace fossil fuels with renewable sources.
repeating coil
    An old name for a transformer, especially used in telephone circuits.
repowering
    Refurbishing the equipment of a power plant, with a view to improved efficiency or life span.
repulsion motor
    A wound rotor induction motor using a pair of short-circuited brushes on a commutator.
resettable fuse
    A circuit protective device that opens on excess current, and then, on cooling off, restores the circuit automatically.
residual current circuit breaker
    A circuit breaker that detects unbalance of phase currents due to ground fault.
resistive circuit
    A circuit containing resistive elements only, no capacitors or inductors.
resistivity
    The property of a material that impedes current flow.
resistor
    A circuit component that primarily has resistance.
resolver
    A transformer-like rotary transducer that measures rotation as an analog value.
resonant cavity
    An opening that when excited by an electron stream or other means, oscillates at a particular frequency.
resonant inductive coupling
    A form of energy transfer between two physically close tuned circuits.
return loss
    A measure of the power loss due to a signal reflection by a discontinuity in a transmission line or an optical fiber.
RF connector
    An electrical fitting used to connect cables carrying radio frequency currents.
RF engineering
    The profession that deals with application of radio frequency energy to useful ends.
rheoscope
    Obsolete name for an ammeter; now an instrument for measuring fluid viscosity.
rheostat
    Obsolete name for a two terminal variable resistor, usually with a rotating shaft to allow manual or motor driven adjustment.
right-hand rule
    A mnemonic device for remembering the definitions of the directions of current and magnetic field in generators.
ripple
    A periodic variation in the amplitude of a DC signal, such as found in a power supply with partly effective filtering.
RLC circuit
    A circuit that has only resistors, inductors, and capacitors in it.
robotics
    The field of automation that deals with manipulators, especially those that mimic human appendages.
robust control
    A static control algorithm that can produce acceptable performance over an anticipated useful range of process disturbances.
Rogowski coil
    A current sensing coil that produces a voltage proportional to the rate of change of current; by integration, this can be turned into a measure of current.
root locus
    A graphical method for analyzing the properties of a transfer function as some parameter is varied.
root mean square
    The root mean square value of a waveform is the DC value that corresponds to equivalent heating value.
rotary converter
    An electric machine that converts electric power between two forms, say, AC and DC or single-phase and three phase, or between two different frequencies of AC (the latter two can be performed by the same machine).
rotary encoder
    A transducer that converts rotation of a shaft to a measurement.
rotary switch
    A switch operated manually or electrically with a rotary motion of the contacts.
rotary transformer
    A transformer used to couple electric signals or power between rotating parts.
rotary variable differential transformer
    A transformer-like transducer that measures rotation as an analog value.
rotor
    That part of an electrical machine that rotates. Not necessarily the armature.
Routh–Hurwitz stability criterion
    A criterion for predicting the stability of a system with a given transfer function.

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S

Sallen–Key filter
    A family of active filters with a second-order characteristic, first described in 1955.
sample and hold
    A circuit that takes a sample of a changing analog value and holds onto it until the value can be processed by some other stage.
sampling
    The process of taking a continually varying signal and turning it into a stream of numbers taken at regular intervals.
sampling frequency
    The rate at which an analog value is sampled.
satellite
    A natural or artificial object that circles another, bound only by gravity.
satellite radio
    A radio broadcasting service using signals from an Earth satellite to customer receivers.
saturation
    That point in the magnetization of a substance where most magnetic domains are aligned with the external field; further increase of the magnetizing force (H) gives only small increase in the magnetization (B).
SCADA
    Supervisory Control and Data Acquisition, management of geographically distributed automation systems such as for an electrical grid.
scattering parameters
    A matrix that describes the electrical behavior of linear electrical networks, most prominently the distributed microwave systems.
Schmitt trigger
    A circuit that behaves like a snap-action switch, suddenly changing state as an analog signal increases; displays hysteresis.
Schottky diode
    A diode that relies on the junction between a semiconductor and a metal.
Scott-T transformer
    A transformer connection for balanced interconnection of a two-phase system and a three-phase system.
s-domain
    A Laplace transform converts a function from the time domain to the "complex frequency" s-domain; making certain mathematical operations much simpler to evaluate.
SDTV
    "Standard definition television" – what descriptions of HDTV call any system with 625 scan lines or less.
segmentation
    A step in digital image processing that groups picture elements of an image that notionally represent some physically significant property of the imaged objects.
selenium rectifiers
    One type of metal rectifier, though selenium is considered a "metalloid" – formerly much used but now replaced by silicon semiconductors.
semiconductor
    A substance with electrical conductivity between that of insulators and conductors; displays a negative temperature coefficient of resistance, and is also sensitive to light. The conductivity of semiconductors can readily be altered by trace amounts of other substances, leading to devices that are the foundation of nearly all modern electronics.
semiconductor device
    A device that relies on substances with electrical conductivity between that of insulators and conductors; the controllable conductivity of these materials makes most of modern electronics possible.
semiconductor fabrication
    The process of turning the raw source of silicon into transistors and integrated circuits.
sensor
    A device or system that converts some physical event into an electronic signal, for further use in measurement or control.
serial communication
    Transmission of data as a single series of bits over a communication path.
series and parallel circuits
    Electrical circuits where current passes through multiple elements either one after the other, or side by side, like the rungs of a ladder, or both.
shaded-pole motor
    An alternating current single-phase motor that produces a rotating magnetic field by a turn of wire around part of a field pole.
shaft voltage
    An objectionable stray voltage that appears on the rotating part of an electrical machine; very deleterious to supporting bearings.
shielded twisted pair
    Two wires, wrapped around each other and covered with a flexible shield conductor; intended to reject external interference.
short-circuit test
    A test of machines or apparatus where the load terminals are directly connected; usually done at reduced power to prevent damage, but destructive short circuit testing may be carried out on circuit protective devices.
short circuit
    A path in a circuit that has negligible resistance; often un-intended, a fault.
shunt
    A small value resistor connected around a metering element to carry most of the current; only a small part passes through the meter.
siemens
    A reciprocal ohm, the SI unit of conductance. The former Siemens mercury unit was a unit of resistance.
signal
    Some intentional modification of a physical communication path that is intended to convey information from one place to another.
signal processing
    The technology to extract information from signals.
signal strength
    A measure of the usable power of a physical signal.
signal-flow graph
    A formal mathematical treatment of the representation of signal flow through a system, such as an analog computer or a radio receiver.
signal-to-noise ratio
    A measure of the power contained in the useful part of the signal, to the power contained in noise. Often measured in decibels; for example, in sound reproduction a 40 or 50 decibel signal to noise ratio would be broadcast quality, whereas a 10 decibel ratio would represent very difficult operating conditions for a voice radio system.
silicon controlled rectifier
    A four layer semiconductor switching device that can stand off an applied voltage until triggered by an electrical pulse on a control lead.
Silicon Valley
    Initially, a region of California known for a large number of electronics technology firms.
sine wave
    The waveform of the mathematical sine function; a fundamental wave shape, free of harmonics.
single-phase electric power
    An alternating current power system using only two wires, where peak voltages in each wire occur at the same time.
single-sideband modulation
    A radio carrier modulation system where redundant frequencies of one duplicate side band are filtered out along with the carrier, to save transmitter power.
skin effect
    The tendency of alternating current to flow at the periphery of a conductor; significant for large conductors at power frequencies, and increasingly significant as the frequency increases.
sliding mode control
    A control strategy for a nonlinear system that uses discontinuous control signals.
slip ring
    A sliding continuous electrical contact between a machine's rotating parts and the fixed external circuit.
small-signal model
    An analytical tool for systems that show significant non-linearity for large signal excursions.
smart grid
    The application of information technology to improve performance of the electrical grid.
Smith chart
    A graphical tool for display of the impedance of devices at varying frequencies, and for solution of problems of impedance matching in radio frequency design.
software engineering
    The profession of designing software systems to meet specified performance requirements.
software
    The set of instructions and data that direct a computer system.
solar cell
    A photovoltaic cell, used to produce power from sunlight.
solar energy
    Useful energy extracted by some means from sunlight.
solar micro-inverter
    An inverter suitable for use with a single solar panel.
soldering
    The process of joining metals using a low melting point filler metal; a critical process in the assembly of most electronic devices.
solenoid
    A coil of wire used to create a magnetic field; often a device with a ferromagnetic plunger that moves when the coil is energized.
solid state
    Electronics that relies on current flow through crystalline lattices.
solid state physics
    That branch of physics that studies arrangements of atoms in fixed arrays.
sound recording
    The technology of recording sound for later reproduction.
space vector modulation
    A control strategy for variable frequency motor drives.
spark spread
    The difference between the revenue from selling a unit of electricity and the cost of the fuel used to make it.
spark-gap transmitter
    A former type of radio transmitter that generated radio frequency current by exciting resonance of a tuned system with an electric spark, used almost entirely for transmission of Morse code.
spectrum analyzer
    An instrument that graphically displays the amplitude of signals in a narrow bandwidth across a frequency band.
speech processing
    The techniques for improving the intelligibility of human speech in a communications system.
SPICE
    A set of computer programs for modelling the behavior of electronic circuits.
split phase distribution
    A type of distribution system that uses a center tapped transformer to provide two voltages to a building wiring system.
split phase motor
    A type of single phase motor that uses a resistor, inductor, or capacitor and two windings to obtain a rotating magnetic field.
square wave
    A waveform that spends equal times at the positive and negative peak values with rapid transitions between them.
stability theory
    The systematic study of control systems that deals with their response to disturbances.
stable polynomial
    That class of polynomials representing the transfer functions of stable control systems.
stacking factor
    A measure of the efficiency of filling the space of a machine core or winding; the proportion of active material in any given unit cross section.
standing wave ratio
    A measure of impedance mismatch for transmission lines in microwave engineering; the ratio of peak amplitude of a standing wave to its minimum.
star-mesh transform
    A mathematical technique used in circuit analysis.
state observer
    In control theory, that which discovers and reports the internal state of a controlled system.
state space representation
    A mathematical technique to represent the internal state of a controlled system as a vector in a Euclidean space.
static VAR compensator
    A system that adjusts reactive power flow without moving parts, such as an electronically controlled capacitor bank.
stator
    That part of a rotating electrical machine that remains stationary.
steady-state
    The condition of a control system where changes due to some disturbance are no longer occurring at a significant rate.
steam turbine
    A rotating machine that converts the energy of expanding steam to mechanical power through its interactions with sets of moving and stationary blades.
step response
    The behavior of a control system in response to an abrupt change of input.
stepper motor
    An electric motor that moves its shafts in discrete steps as different poles are energized.
stereophonic sound
    Sound reproduction systems intended to reproduce sound emanating from more than one direction.
Stokes' theorem
    A theorem about integration of three-dimensional functions, much used in analysis of electric fields.
storage tube
    A type of cathode ray tube, used for storing images or data.
stray capacitance
    A property of every conductor, when considered as a non-ideality.
structured cabling
    A system for design of the telephone and data communications cable systems of a building.
submarine communications cable
    A telephone or telegraph cable that is substantially under water.
sulfur hexafluoride circuit breaker
    A kind of automatic circuit protection switch that breaks current in an atmosphere of pressurized sulfur hexafluoride gas to extinguish the arc.
super grid
    A wide area power transmission network that allows interchange over continental distances.
supercomputer
    A computer with a substantially higher level of performance than a general-purpose machine; especially adapted for high intensity calculation on large data sets.
superconducting electric machine
    An experimental type of generator or motor that has part of its electric circuits in the superconducting state.
superconductivity
    The loss of all electrical resistance at inconveniently low temperatures.
superheterodyne receiver
    A radio receiver that changes incoming frequencies to a fixed intermediate frequency for processing.
superposition theorem
    The useful property of a system where the response to the sum is the sum of the responses.
surge arrester
    A device intended to absorb brief transient overvoltages to protect machines or apparatus.
surge protection
    The measures taken to protect machines and apparatus from transient overvoltages.
switch
    An electrical device that opens and closes a circuit; it may be manually operated, automatically operated by some other electrical circuit, or operated by the change in some physical condition such as flow, level, or temperature.
switched reluctance motor
    A motor that relies on induced magnetism in salient poles, instead of a rotor winding.
switched-mode power supply
    A power converter that regulates voltage by adjusting the time duration of a switching device; this gives reduced heat dissipation compared to an equivalent linear regulator device.
switchgear
    An array of switches, circuit breakers and related apparatus for power distribution.
symbolic circuit analysis
    Analytical circuit analysis in terms of expressions with variables, instead of numerical solutions for a particular case of values.
symmetrical components
    A technique to simplify analysis of unbalanced polyphase systems.
synchro
    A synchromotor, a class of electrical motors that follows the rotation of a source.
synchronization
    Aligning the timing of two or more sources, such as synchronizing a generator before connecting it to a grid.
synchronous circuit
    A logic circuit where internal state changes only propagate in step with a master clock signal.
synchronous motor
    A motor that rotates at a speed exactly related to the supply frequency.
synchronous rectification
    A converter from alternating to direct current, where switching devices actively are operated in step with the positive and negative excursions of the supply.
synchroscope
    An instrument used to bring an alternating current generator into synchronization with a grid, that uses a moving pointer or set of lamps.
system identification
    The technique of development of a mathematical model of a controlled system; model identification.
system on a chip
    An integrated circuit that combines multiple significant subsystems of a product on one die, for example, analog signal processing and digital controls.
system on module
    A packaging of significant functions of a complete product in a form that can be used in more than one product.

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T

tachometer
    An instrument that measures rotational speed (or angular velocity).
tap
    A connection to a winding at some point between the ends, used to adjust voltage.
tap changer
    A switch that selects which transformer tap is connected to an external circuit; may be manually operated, or power operated; some types can be operated under load for voltage regulation purposes.
technical drawing
    Drawings intended to convey information for construction, operation or maintenance of a system or equipment.
telecommunication
    The field that deals with transmission of information over distances longer than can be covered by an unaided human.
Telecommunications Industry Association
    A US based trade association that develops technical standards.
telegraph
    A system for transmitting text messages, by wire or other means.
telegrapher's equations
    Coupled linear partial differential equations that relate the voltage and current on a transmission line.
telephone balance unit
    A balun, a transformer used to convert between balanced and unbalanced lines, as used in telephone circuits.
telephone line
    Outside plant that connects a central office to subscriber equipment.
telephone
    Transmission of voice by electrical means.
television
    Transmission of moving images by electrical means.
Tellegen's theorem
    A theorem relating to branch currents in an electrical network.
tesla
    The SI unit of magnetic flux density.
Tesla coil
    A kind of resonant transformer capable of very high voltages; almost identical to an Oudin coil except that it has separately wound primary and secondary.
tetrode
    An electron device, nearly always a vacuum tube, with four internal active electrodes.
thermionic emission
    Emission of electrons from a hot surface; the Edison Effect was an early instance of description of this phenomenon.
thermistor
    A temperature sensitive resistor with a large, somewhat variable, temperature coefficient of resistance.
thermocouple
    A junction of two dissimilar metals that generates voltage when at a temperature above absolute zero.
thermoelectric effect
    The conversion between heat flow and current flow, and the reverse.
thermostat
    A temperature sensing switch.
Thévenin theorem
    A theorem which states that any network of current sources, voltage sources and resistors can be simplified to an equivalent network with only a voltage source and series impedance; the dual of Norton's Theorem.
third rail
    An energized conductor in the track bed, using a sliding contact to transfer power to an electric train.
three-phase AC railway electrification
    Application of three-phase power to railways.
three-phase electric power
    Electric power transmission using three conductors carrying currents which peak at separate evenly spaced times in each cycle; widely used for motors.
thyristor
    A four layer semiconductor device that stands off applied voltage until triggered.
thyristor drive
    A variable speed drive, usually with direct current motors, using thyristors as the switching elements.
tidal power
    Extraction of useful energy, usually as electric power, from the tidal rise and fall of water.
time sharing
    A system whereby multiple human users of a computer can proceed as if they had sole use, while the computer processes each user's software in round-robin fashion.
time-invariant system
    A systems whose characteristics don't vary significantly with time.
topology
    The shape of an electrical network, independent of its size or values.
toroidal inductors and transformers
    Magnetic coils wound around a ring of ferromagnetic material.
total harmonic distortion (THD)
    A measure of the magnitude of harmonically-related frequency components a signal processing stage adds.
traction battery
    A battery used to store energy for propelling a wheeled electric vehicle.
traction current
    Power supply for wheeled electric vehicles.
traction motor
    An electric motor for a wheeled vehicle.
traction substation
    A substation that supplies current to a railway, subway or similar electric wheeled transit.
transatlantic communications cable
    A cable for voice or data running under the Atlantic Ocean.
transceiver
    Apparatus that combines a receiver and transmitter.
transconductance
transducer
    An instrument that converts a physical quantity into another electrical or physical quantity.
transfer function
    The mathematical relation between input and output, usually expressed in terms of frequency or complex frequency (s-domain).
transformer oil testing
    Examination of transformer oil for its insulating strength, dissolved moisture and other properties, to ensure it is still suitable for use.
transformer oil
    A hydrocarbon liquid that cools and insulates transformers and other types of electrical apparatus.
transformer
    A static arrangement of conductors and possibly magnetic materials, that transfers energy by electromagnetic induction.
transformerboard
    A kind of insulating paperboard used for internal structures of large oil filled power transformers.
transient response
    The short-time response of a system to a disturbance.
Transil
    A brand of transient voltage suppression diode.
transistor
    A three terminal solid state device used as an amplifier or switch.
transmission
    The process of getting a signal from one point to another.
transmission line
    An arrangement of conductors for movement of electric power; used from DC to upper radio frequencies.
transmission system operator
    A corporation that runs the transmission system between sources of power and distribution substations.
transmission tower
    A structure for support of overhead transmission wires.
transmitter
    Apparatus that prepares a signal for emission into some medium, such as a radio transmitter or a sonar transmitter.
traveling-wave tube
    A type of microwave amplifier vacuum tube.
trembler coil
    A kind of high-voltage coil that includes an interrupting mechanism, formerly used in automobile ignition systems.
TRIAC
    A variation of the thyristor that can pass bidirectional (ac) current.
triangle wave
    A waveform composed of straight-line segments that extend from minus peak to plus peak.
trigger transformer
    A transformer that generates a pulse to initiate some other device, such as a thyristor or a flash tube.
triode
    An electron device, nearly always a vacuum tube, that has three active electrodes.
trolley pole
    A support for a current collector on a vehicle.
trolleybus
    Strictly, a passenger vehicle that collects motive electric power from a pair of overhead conductors.
tuned circuit
    A circuit that displays a peak response at some frequency.
twisted pair
    Two wires twisted around each other, possibly covered with an overall sheath; this configuration rejects some kinds of interference.
two-phase electric power
    An electric power system using two sets of alternating currents, displaced in time by a quarter period.
two-port network
    A network that has two places to exchange energy with its surroundings.
two-sided Laplace transform
    A variant of the Laplace transform that simplifies certain operations.

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U

ubiquitous computing
    A scenario where computer science is made to appear everywhere.
ultrasonic motor
    A motor that relies on a component oscillating at an ultrasonic frequency.
ultrasonics
    Term for the field of study pertaining to pressure oscillations in air or other media that are above the range of human hearing.
ultrasound
    Sound having a frequency above the range of normal human hearing. A portmanteau of the former description of 'ultrasonic sound'
undersampling
    Sampling a signal at less than the Nyquist rate; can produce alias frequencies or other artifacts.
unijunction transistor
    A three terminal semiconductor device with a definite switching characteristic and only one PN junction.
unipolar motor
    A heteropolar motor; all currents in this design flow in only one direction.
unshielded twisted pair
    Two wires wrapped around each other, but without a conductive cover.
upsampling
    Sampling at greater than the Nyquist rate, which makes filter design easier.
utility frequency
    60 or 50 cycles per second, used for electric power.
utility pole
    A columnar structure that carries wires for electrical power distribution, cable television, telephone or similar services.

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V

vacuum capacitor
    A capacitor using vacuum as its dielectric; useful at high voltages or radio frequency.
vacuum tube
    An electron device that relies on flow of electrons through a vacuum or low-pressure gas; a valve. The first electronic devices that could amplify.
valve
    A switching element (mercury arc, thyristor, or other device) in a high-voltage direct current converter; each phase contains two or more valves, which may be series-connected for higher voltages. Or, a vacuum tube.
variable capacitor
    A capacitor whose value can be changed, by rotating a shaft, squeezing a plate or by an electrical signal; for example, as used to tune a radio.
variable-frequency drive
    A power converter that varies the speed of an AC motor by changing its frequency; usually, today, a solid-state device.
Variac
    One brand of adjustable transformer, that can essentially continuously vary the ratio between primary and secondary.
varicap
    Variable capacitor – usually a diode whose reverse-biased junction capacitance can be varied by applied voltage.
varistor
    Variable resistor – a protective device that has a high resistance at low voltage but momentarily switches to lower resistance on exposure to a high voltage.
vector control
    A strategy for control of variable-speed motor drives.
vector group
    The classification of the connections of a polyphase transformer.
vehicle-to-grid
    A concept to use electric vehicle batteries as a form of grid energy storage.
vehicular automation
    Automatic systems to assist, or replace, the driver of a vehicle.
Versorium
    An antique version of an electroscope.
vibrator
    An electromechanical interrupter, part of a DC-to-AC converter in a battery-operated vacuum tube radio, or similar application. Some had additional contacts to act as a synchronous rectifier.
video camera tube
    A family of vacuum tube devices used to pick up images and transmit them electronically.
video processing
    The techniques used to enhance video images.
virtual instrumentation
    A software-intensive measuring system that can be programmed to emulate any of a number of conventional measuring instruments, or some combination of measuring functions.
virtual power plant
    A strategy for managing a collection of disparate power sources, interconnected with a communications network, as if they were a single centralized power plant.
VLSI
    Very Large Scale Integration, the ability to put hundreds of thousands of interconnected transistors onto one chip.
volt
    The SI unit of electrical potential difference; moving a charge of one coulomb through a potential of one volt transfers one joule of energy.
voltage
    The electric potential difference between two points.
voltage compensation
    Generally, adjustment of a voltage source to compensate for voltage drop; techniques differ widely between a computer power supply and a long-distance power line.
voltage-controlled amplifier
    An amplifier that has its gain controlled by a voltage signal.
voltage controller
    A device that adjusts the (effective) voltage to a load.
voltage converter
    Any device that changes electric power at one voltage to power at a second; a transformer is a common example of an AC voltage converter.
voltage division
    A circuit that produces an output voltage that is some, perhaps adjustable, fraction of the input voltage.
voltage doubler
    A rectifier circuit that can product an output DC voltage of nearly twice the input AC voltage.
voltage regulation
    A measure of how a source maintains its output voltage for varying load.
voltage regulator
    A system that automatically stabilizes the voltage at which power is supplied to a downstream system.
voltage source
    In circuit theory, a hypothetical element that maintains a specified voltage between its terminals independent of the current through it.
voltage spike
    A transient electrical voltage higher than normal appearing on an electrical supply.
voltage-to-current converter
    A circuit that produces an output current proportional to an input voltage.
volt-ampere
    The unit of apparent power in an AC circuit.
voltmeter
    An instrument for measuring potential difference.

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W

war of the currents
    The late 19th century commercial dispute on whether AC or DC was the best system for power distribution.
Ward Leonard control
    A speed control system for DC machines using an interconnected generator and motor.
watt
    The SI unit of power, work done per unit time.
wattmeter
    An instrument that measures electrical power.
waveguide
    A tubular structure that guides electromagnetic waves, much used at microwave frequencies; an optical fiber is a kind of optical waveguide.
weber
    The SI unit of magnetic flux.
wet transformer
    In telephone systems, a matching transformer that can operate while carrying a substantial DC "wetting" current.
Wien bridge oscillator
    A type of electronic oscillator that generates sine waves and is based on a bridge circuit.
Wiener filter
    A class of filters used in signal processing, used to fit an estimate to noisy signal data.
Williams tube
    A cathode ray vacuum tube used as an early form of computer memory.
wind farm
    An array of two or more wind turbines, usually sharing a substation.
wind power
    Generation of electricity (sometimes mechanical power) from wind.
wind turbine
    A rotating machine that extracts energy from wind.
wire
    A strand of metal much, much, longer than it is wide; a conductor, often coated with insulation.
wireless network
    Data network relying on radio for the connection to end device; may span a building or a larger area.
wireless telegraphy
    Transmission of text by radio; usually implies Morse or radio-teletype.

X

X-ray
    Electromagnetic radiation with wavelengths shorter than ten nanometres. Strictly: radiation that is produced in the electron shell of atoms.
X-ray lithography
    A developing technique for production of very high density structures in integrated circuits.

Y

Yagi antenna
    A type of radio antenna using a feeder element, one or more parasitic reflector elements, and one or more director parasitic elements to provide a directional characteristic; the classic home TV rooftop antenna was usually a Yagi antenna .
Y-delta transform
    A mathematical technique in circuit analysis to simplify a circuit.

Z

Zener diode
    Nickname for "voltage regulator diodes" which may rely either on the Zener effect or avalanche breakdown to maintain a roughly constant voltage; the two effects have opposite temperature coefficients of voltage.
zigzag transformer
    A multiwinding three phase transformer, sometimes used for grounding.
Z-transform
    A mathematical operation that converts a set of evenly spaced measurements of an analog signal into a series of frequency components.

 

 

 A

Adenosine Triphosphate (ATP)
    A chemical compound that functions as fuel for biomolecular nanotechnology.
Animat
Assembler
    A molecular manufacturing device capable of positioning molecules through chemical reactions.
Atom
    The smallest unit of a chemical element, about a third of a nanometer in diameter.
Atomic force microscope (AFM)
    An imaging instrument used to “magnify” at the molecular level through mechanical tracing of surface contours.
Automated engineering
    Engineering done by computer systems without the input of humans.
Automated manufacturing
    Manufacturing at the nano-level by assemblers & Replicators by themselves.
Atomic layer deposition (ALD)
    A technique developed in the 1970s for depositing monolayers of material in a sequential, controlled manner using self-limiting reactions. It is used to make thin films.
Atomic Manipulation
    Manipulating atoms, typically with the tip of an STM.
Atomistic Simultations
    Atomic motion computer simulations of macromolecular systems are increasingly becoming an essential part of materials science and nanotechnology.

B

Ballistic Magnetoresistance (BMR)
    A way in which spin orientation, encoding information on a storage medium such as a hard drive, can modify electrical resistance in a nearby circuit, thereby accomplishing the sensing of that orientation.
Bio-assemblies
    Containing several protein units, DNA loops, lipids, various ligands, etc.
Biovorous
    An organism capable of converting biological material into energy for sustenance.
Biochauvinism
    The prejudice that biological systems have an intrinsic superiority that will always give them a monopoly on self-reproduction and intelligence.
Biomedical Nanotechnology
BioMEMS
    MEMS used in medicine, that use microchips.
BioNEMS
    Biofunctionalized nanoelectromechanical systems.
Biomimetics
    Study of the structure and function of biological substances to make artificial products that mimic the natural ones.
Biomimetic Chemistry
    Knowledge of biochemistry, analytical chemistry, polymer science, and biomimetic chemistry is linked and applied to research in designing new molecules, molecular assemblies, and macromolecules having biomimetic functions.
Biomimetic Materials
    Materials that imitate, copy, or learn from nature.
Biopolymeroptoelectromechanical Systems (BioPOEMS)
    Combining optics and microelectromechanical systems, and used in biological applications.
Biostasis
    A condition in which an organism's cell and tissue structure are preserved, allowing later restoration by cell repair machines.
Blue goo
    Slang term for nanobots designed to protect against harmful nanotechnology; "blue" being a metonym for police as in the color of many police uniforms.
Bose-Einstein Condensate (BEC)
    A state of matter (also called the fifth state of matter) which is typically formed when a gas of bosons at low densities is cooled to temperatures very close to absolute zero.
Bottom Up
    Building larger objects from smaller building blocks. Nanotechnology seeks to use atoms and molecules as those building blocks.
Brownian Assembly
    Brownian motion in a fluid brings molecules together in various position and orientations.
Brownian Motion
    Motion of a particle in a fluid owing to thermal agitation, observed in 1827 by Robert Brown.
Bulk technology
    Technology in which atoms and molecular are manipulated in bulk, rather than individually.
Buckminsterfullerene
    A broad term covering the variety of buckyballs and carbon nanotubes that exist.
Bucky Balls
    Molecules made up of 60 carbon atoms arranged in a series of interlocking hexagonal shapes, forming a structure similar to a soccer ball.
Bush robot
    A concept for robots of ultimate dexterity, they utilize fractal branching to create ever-shrinking "branches," eventually ending in nanoscale "fingers."

C

Carbon Nanotubes
Cellular Automata
    an array of identically programmed automata, or "cells," which interact with one another.
Cell pharmacology
    Delivery of drugs by medical nanomachines to exact locations in the body.
Cell Repair Machine
    Molecular and nanoscale machines with sensors, nanocomputers and tools, programmed to detect and repair damage to cells and tissues, which could even report back to and receive instructions from a human doctor if needed.
Chemical Vapour Deposition (CVD)
    A technique used to deposit coatings, where chemicals are first vaporized, and then applied using an inert carrier gas such as nitrogen.
Cobots
    Collaborative robots designed to work alongside human operators.
Cognotechnology
    Convergence of nanotech, biotech and IT, for remote brain sensing and mind control.
Computational Nanotechnology
    Permits the modeling and simulation of complex nanometer-scale structures.
Computronium
    A highly (or optimally) efficient matrix for computation, such as dense lattices of nanocomputers or quantum dot cellular automata.
Contelligence
    The combination of awareness and computational power required in an Artificially Intelligent network before we could, without loss of anything essential, upload ourselves into them.
Convergent Assembly
    It is based on the idea that smaller parts can be assembled into larger parts, larger parts can be assembled into still larger parts, and so forth.

D

Dendrimers
    A tiny molecular structure that interacts with cells, enabling scientists to probe, diagnose, cure or manipulate them on a nanoscale.
Diamondoid
    Structures that resemble diamond in a broad sense, strong stiff structures containing dense, three dimensional networks of covalent bonds, formed chiefly from first and second row atoms with a valence of three or more.
Dip Pen Nanolithography
    An AFM-based soft-lithography technique.
Directed-Assembler
    A specific type of assembler that makes use of directed-assembly, such that the assembly process requires external energy or information input.
Disassemble
    An instrument able to take apart structures a few atoms at a time, recording structural information at each step.
DNA Chip
    A purpose built microchip used to identify mutations or alterations in a gene's DNA.
Dopeyballs
    Superconducting Buckyballs (they) have the highest critical temperature of any known organic compound.
Dry Nanotechnology
    Derives from surface science and physical chemistry, focuses on fabrication of structures in carbon (e.g. fullerenes and nanotubes), silicon, and other inorganic materials.

E

Ecophagy
    Consuming the biological environment.
Ecosystem protector
    A nanomachine for mechanically removing selected imported species from an ecosystem to protect native species.
Enabling science and technologies
    Areas of research relevant to a particular goal, such as nanotechnology.
Entanglement
    From quantum mechanics, entanglement is a relationship between two objects in which they both exhibit superposition but once the state of one object is measured, the state of the other is also known.
Exponential assembly
    A manufacturing architecture starting with a single tiny robotic arm on a surface.
Exponential Growth
    Exponential growth refers to the process of growth or replication involving doubling within a given period.

F

Femtometer
    A unit suitable to express the size of atomic nuclei.
Femtosecond
    One quadrillionth of a second, and is to a second what a second is to 32,700,000 years.
Femtotechnology
    The art of manipulating materials on the scale of elementary particles (leptons, hadrons, and quarks).
Fluidic Self Assembly
    A novel technique for accurately assembling large numbers of very small devices.
Foglet
    A mesoscale machine.
Fractal
    A mathematical construct that has a fractional dimension.
Fractal Mechatronic Universal Assembler
    A machine that is capable of assembling any chemical from a generic descriptions of the properties required of the chemical.
Fractal Robots
    Programmable machines that can do unlimited tasks in the physical world, the world of matter.
Fullerenes
    A molecular form of pure carbon discovered in 1985.

G

Genegeneering
    Genetic engineering.
GENIE
    An AI combined with an assembler or other universal constructor, programmed to build anything the owner wishes. Sometimes called a Santa Machine.
Golden goo
    Hypothetical scenario in which nanomachines programmed to filter gold from seawater go out of control and produce endless piles of gold goo.
GNR technologies
    Genetic Engineering, Nanotechnology, and Robotics.
Grey goo
    Hypothetical global catastrophic scenario involving molecular nanotechnology in which out-of-control self-replicating machines consume all biomass on Earth while building more of themselves.
Green goo
    Hypothetical use of nanomachines or bio-engineered organisms used for population control of humans, either by governments or eco-terrorist groups.
Guy Fawkes scenario
    Hypothetical scenario in which wide availability of nanotech makes it trivial for anyone to produce significant amounts of explosives for use in committing acts of terrorism.

H

Heteronuclear
    Consisting of different elements.

I

Immune Machines
    Medical nanomachines designed for internal use, especially in the bloodstream and digestive tract, able to identify and disable intruders such as bacteria and viruses.
IMP
    Electronic implant, especially in the brain.
Inline Universities
    Nanocomputer implants serving to increase intelligence and education of their owners, essentially turning them into walking universities.

K

Khaki goo
    Slang term for hypothetical military use of nanotechnology, especially as of weaponized grey goo.
Knowbots
    Knowledge robots, first developed Vinton G. Cref and Robert E. Kahn for National Research Initiatives.

L

Langmuir-Blodgett
    The name of a nanofabrication technique used to create ultrathin films (monolayers and isolated molecular layers), the end result of which is called a "Langmuir-Blodgett film."
LCD
    The predominant technology used in flat panel displays.
LED
OLED
Limited Assembler
    Assembler capable of making only certain products; faster, more efficient, and less liable to abuse than a general-purpose assembler.

M

Mechanochemistry
    The direct, mechanical control of molecular structure formation and manipulation to form atomically precise products.
Mechanosynthesis
    Molecular tools with chemically specific tip structures can be used, sequentially, to modify a work piece and build a wide range of molecular structures.
Microelectromechanical systems (MEMS)
    Generic term to describe micron scale electrical/mechanical devices.
Mesoscale
    A device or structure larger than the nanoscale (10^-9 m) and smaller than the megascale.
Microencapsulation
    Individually encapsulated small particles.
Molecular assembler
    Also known as an assembler, a molecular assembler is a molecular machine that can build a molecular structure from its component building blocks.
Molecular Beam Epitaxy
    Process used to make compound (multi-layer) semiconductors.
Molecular Integrated Microsystems (MIMS)
    Microsystems in which functions found in biological and nanoscale systems are combined with manufacturable materials.
Molecular Electronics (ME)
    Any system with atomically precise electronic devices of nanometer dimensions, especially if made of discrete molecular parts rather than the continuous materials found in today's semiconductor devices.
Molecular Manipulator
    A device combining a proximal probe mechanism for atomically precise positioning with a molecule binding site on the tip; can serve as the basis for building complex structures by positional synthesis.
Molecular Manufacturing
    Manufacturing using molecular machinery, giving molecule-by-molecule control of products and by-products via positional chemical synthesis.
Molecular Medicine
    Studying molecules as they relate to health and disease, and manipulating those molecules to improve the diagnosis, prevention, and treatment of disease.
Molecular Nanogenerator
Molecular Nanotechnology (MNT)
    Thorough, inexpensive control of the structure of matter based on molecule-by-molecule control of products and byproducts; the products and processes of molecular manufacturing, including molecular machinery.
Molecular Recognition
    A chemical term referring to processes in which molecules adhere in a highly specific way, forming a larger structure; an enabling technology for nanotechnology.
Molecular Systems Engineering
    Design, analysis, and construction of systems of molecular parts working together to carry out a useful purpose.
Molecular Wire
    A molecular wire - the simplest electronic component - is a quasi-one-dimensional molecule that can transport charge carriers (electrons or holes) between its ends.
MOLMAC
    Molecular machine.
Monomer
    The units from which a polymer is constructed.
Monomolecular Computing
    The implantation inside a single molecule of all the functional groups or circuits to realize a calculation, without any help from external artifices such as re-configuration, calculation sharing between the user and the machine, or selection of the operational devices.
Moore's Law
    It stated at the time that the number of transistors packed into an integrated circuit had doubled every year since the technology's inception four years earlier.

N

Nanarchist
    Someone who circumvents government control to use nanotechnology, or someone who advocates this.
Nanarchy
    The use of automatic law-enforcement by nanomachines or robots, without any human control.
Nanoarray
    An ultra-sensitve, ultra-miniaturized array for biomolecular analysis.
Nanoassembler
Nanobalance
    A nanoscale balance for determining mass, small enough to weigh viruses and other sub-micron scale particles.
Nanobeads
    Polymer beads with diameters of between 0.1 to 10 micrometers.
Nanobialys
    Miniature bialy-shaped particles developed by Washington University as delivery agents for drugs and imaging agents directly to the sites of tumors and plaques.
Nanobiotechnology
    Applying the tools and processes of MNT to build devices for studying biosystems, in order to learn from biology how to create better nanoscale devices.
Nanobot
Nanobubbles
    Tiny air bubbles on colloid surfaces.
Nanocatalysis
Nanochips
Nanochondria
    Nanomachines existing inside living cells, participating in their biochemistry (like mitochondria) and/or assembling various structures.
Nanocombinatorics
    The new analytical method utilizes a technique invented at Northwestern called polymer pen lithography, where basically a rubber stamp having as many as 11 million sharp pyramids is mounted on a transparent glass backing and precisely controlled by an atomic force microscope to generate desired patterns on a surface.
Nanocomputer
    A computer made from components (mechanical, electronic, or otherwise) built at the nanometer scale.
Nanocontainers
    Nanoscale polymeric containers that could be used to selectively deliver hydrophobic drugs to specific sites within individual cells.
Nanocrystals
    Aggregates of anywhere from a few hundred to tens of thousands of atoms that combine into a crystalline form of matter known as a "cluster."
Nanodefenses
    Any of the "good" goos, such a blue goo; protectors against grey goo, destructive nanoswarms, and the like.
Nanodisaster
    Various so-called "goo" scenarios that have potentially negative outcomes.
NEMSA
    A generic term to describe nano scale electrical/mechanical devices.
Nanoelectronics
    Electronics on a nanometer scale, whether made by current techniques or nanotechnology; includes both molecular electronics and nanoscale devices resembling today's semiconductor devices.
Nanofabrication
    Construction of items using assemblers and stock molecules.
Nanofacture
    The fabrication of goods using nanotechnology.
Nanofilters
    One opportunity for nanoscale filters is for the separation of molecules, such as proteins or DNA, for research in genomics.
Nanofluidics
    Controlling nano-scale amounts of fluids.
Nanogate
    A device that precisely meters the flow of tiny amounts of fluid.
Nanohorns
    One of the SWNT (single walled carbon nanotube) types, with an irregular horn-like shape, which may be a critical component of a new generation of fuel cells.
Nanoimprinting
    A technique that is very simple in concept, and totally analogous to traditional mould- or form-based printing technology, but that uses moulds (masters) with nanoscale features.
Nanoimprint Machine
    A form of soft lithography.
Nanohacking
    "Hacking" at the molecular level.
Nanoindentation
    Similar to conventional hardness testing performed on a much smaller scale.
Nanolithography
    Writing on the nanoscale.
Nanomachine
    An artificial molecular machine of the sort made by molecular manufacturing.
Nanomachining
    Like traditional machining, where portions of the structure are removed or modified, nanomachining involves changing the structure of nano-scale materials or molecules.
nanoManipulator
    Uses virtual reality (VR) goggles and a force feedback probe as an interface to a scanning probe microscope, providing researchers with a new way to interact with the atomic world.
Nanomanipulation
    The process of manipulating items at an atomic or molecular scale in order to produce precise structures.
Nanomanufacturing
Nanomaterials
    Can be subdivided into nanoparticles, nanofilms and nanocomposites.
Nanomedicine
Nano-Optics
    Interaction of light and matter on the nanoscale.
Nanopens & Nanopencils
    Allows for drawing electronic circuits a thousand times smaller than current ones.
NanoPGM
Nanopharmaceuticals
    Nanoscale particles used to modulate drug transport for drug uptake and delivery applications.
Nanophase Carbon Materials
    A form of matter in which small clusters of atoms form the building blocks of a larger structure.
Nanoplotter
    A multi-tip nanopen.
Nanopores
    Involves squeezing a DNA sequence between two oppositely charged fluid reservoirs, separated by an extremely small channel.
Nanoprobe
    Nanoscale machines used to diagnose, image, report on, and treat disease within the body.

P

Picotechnology
    The art of manipulating materials on a quantum scale.
POSS Nanotechnology
    POSS nanomaterials are attractive for missile and satellite launch rocket applications because they offer effective protection from collisions with space debris and the extreme thermal environments of deep space and atmospheric re-entry.
Polysilicon
    Used in the manufacture of computer chips.
Positional Controlled Chemical Synthesis
    Control of chemical reactions by precisely positioning the reactive molecules, the basic principle of assemblers.
Positional Assembly
    Constructing materials an atom or molecule at a time.
Protein Design
    The design and construction of new proteins; an enabling technology for nanotechnology.
Protein folding
    The process by which proteins acquire their functional, preordained, three-dimensional structure after they emerge, as linear polymers of amino acids, from the ribosome.
Proteomics
    The term proteome refers to all the proteins expressed by a genome, and thus proteomics involves the identification of proteins in the body and the determination of their role in physiological and pathophysiological functions.

Q

Quantum Computer
    A computer that takes advantage of quantum mechanical properties such as superposition and entanglement resulting from nanoscale, molecular, atomic and subatomic components.
Quantum Confined Atoms (QCA)
    Atoms caged inside nanocrystals.
Quantum Cryptography
    A system based on quantum- mechanical principles.
Quantum Dots
    Nanometer-sized semiconductor crystals, or electrostatically confined electrons.
Quantum Dot Nanocrystal (QDN)
    Used to tag biological molecules, and "measuring between five and ten nanometres across, are made up of three components.
Quantum Mechanics
    A largely computational physical theory explaining the behavior of quantum phenomena, which incorporates the theory of special relativity. Despite dilignet attempts, general relativity has not been successfully incorporated into quantum mechanics.
Quantum Mirage
    A nanoscale property that may allow information to be transferred through use of the wave property of electrons.
Quantum Tunneling
    When electrons pass through a barrier, without overcoming it or breaking it down.
Quantum well
    A P-N-P junction in which the "N" layer is ~10 nm (where traditional physics leaves off and quantum effects take over) and an "electron trap" is created.
Quantum wire
    Another form of quantum dot, but unlike the single-dimension "dot," a quantum wire is confined only in two dimensions.
Qubit
    The quantum computing analog to a bit.

R

Red goo
    Nanotechnology which is deliberately designed and released to cause harm, as opposed to a grey goo scenario which is assumed to be accidental.
Replicator
    A system able to build copies of itself when provided with raw materials and energy.
Rheology
    The study of the deformation and flow of matter under the influence of an applied stress, which might be, for example, a shear stress or extensional stress.

S

SAMFET
    Where a few molecules act as FETs, exhibiting both very strong gain, and extraordinarily rapid response.
Scanning Capacitance Microscopy
    A method for mapping the local capacitance of a surface.
Scanning Force Microscope (SFM)
    An instrument able to image surfaces to molecular accuracy by mechanically probing their surface contours.
Scanning Near Field Optical Microscopy
    A method for observing local optical properties of a surface that can be smaller than the wavelength of the light used.
Scanning Thermal Microscopy
    A method for observing local temperatures and temperature gradients on a surface.
Scanning Tunneling Microscope (STM)
    An instrument able to image conducting surfaces to atomic accuracy; has been used to pin molecules to a surface.
Sealed Assembler Laboratory
    A work space, containing assemblers, encapsulated in a way that allows information to flow in and out but does not allow the escape of assemblers or their products.
Self-assembly
    In chemical solutions, self-assembly (also called Brownian assembly) results from the random motion of molecules and the affinity of their binding sites for one another.
Self-repair
    Indicating ability to heal itself without outside intervention.
Self-replication
    More accurately labeled "exponential replication," self-replication refers to the process of growth or replication involving doubling within a given period.
Single-walled carbon nanotubes (SWNT)
Shape Memory Alloy
    A unique class of alloys which are able to "remember" their shape and are able to return to that shape even after being bent.
Smartdust
    Tiny, bottle-cap-shaped micro-machines fitted with wireless communication devices - that measure light and temperature.
Smart material
    Materials and products capable of relatively complex behavior due to the incorporation of nanocomputers and nanomachines.
Spintronics
    Electronic devices that exploit the spin of electrons as well as their charge.
Superconductor
    An object or substance that conducts electricity with zero resistance.
Superlattice Nanowire Pattern
    A technique for producing "Ultra High Density Nanowire Lattices and Circuits". See Researchers Discover How to Make the Smallest, Most Perfect, Densest Nanowire Lattices-And It's a SNAP
Superposition
    A quantum mechanical phenomena in which an object exists in more than one state simultaneously.
Superlattice Nanowire
    Interwoven bundles of nanowires using substances with different compositions and properties.

T

Technocyte
    A nanoscale artificial device (especially a nanite) in the human bloodstream used for repairs, cancer protection, as an artificial immune system or for other uses.
Top Down Molding
    Carving and fabricating small materials and components by using larger objects such as our hands, tools and lasers.
Transistor
    The basic element in an integrated circuit.

U

Universal Assembler
    Uses raw atoms and molecules to construct consumer goods, and is pollution free.
Universal Constructor
    A machine capable of constructing anything that can be constructed.
Utility fog
    Objects formed of "intelligent" polymorphic (able to change shape) substances, typically having an octet truss structure.

V

Vasculoid
    A single, complex, multisegmented nanotechnological medical robotic system capable of duplicating all essential thermal and biochemical transport functions of the blood, including circulation of respiratory gases, glucose, hormones, cytokines, waste products, and cellular components.
Von Neumann Machine
    A machine which is able to build a working copy of itself using materials in its environment.
Von Neumann Probe
    A von Neumann Machine able to move over interstellar or interplanetary distances and to utilize local materials to build new copies of itself.

W

Wet nanotechnology
    The study of biological systems that exist primarily in a water environment.

Z

Zeptosecond
    One-billion-trillionth of a second.
Zettatechnology
    Referring to the typical number of distinct designed parts in a product made by the systems we envision (molecular, mature, or molecular-manufacturing-based nanotechnology).

 

 

 A
abreaction

Abreaction is a process of vividly reliving repressed memories and emotions related to a past event.[1] Sigmund Freud used hypnosis to rid his patients of pathological memories through abreaction.[1]
abulia

Aboulia or Abulia, in neurology, refers to a lack of will or initiative. The individual is unable to act or make decisions independently. The condition may range from subtle to overwhelming in severity.
achromatopsia

Achromatopsia is a term referring to or acquired agnosia for color. This term includes color blindness. Achromatopsia is a condition characterized by a partial or total absence of color vision. People with complete achromatopsia cannot perceive any colors; they see only black, white, and shades of gray. Incomplete achromatopsia is a milder form of the condition that allows some color discrimination.

Achromatopsia also involves other problems with vision, including an increased sensitivity to light and glare (photophobia), involuntary back-and-forth eye movements (nystagmus), and significantly reduced sharpness of vision (low visual acuity). Affected individuals can also have farsightedness (hyperopia) or, less commonly, nearsightedness (myopia). These vision problems develop in the first few months of life.

Achromatopsia is different from the more common forms of color vision deficiency (also called color blindness), in which people can perceive color but have difficulty distinguishing between certain colors, such as red and green.[2]
affect illusion

Illusions, or misperceptions associated with or based on changes with mood; for example, at midnight a person may take a shadow as a ghost, but in the early part of night this may not be the case.
akataphasia

Akataphasia (Kraepelin 1896) refers to a syntactic disturbance of speech resulting from dissolution of logical ordering of thoughts. It manifests as rambling speech. Compare Derailment.[3]
akathisia
Main article: Akathisia

Akathisia refers to a subjective feeling of restlessness in the lower limbs that is related to abnormal activity in the extrapyramidal system in the brain, often due to antipsychotic medication.[1] It tends to manifest as an inability to sit still.[1]
alexithymia
Main article: Alexithymia

Alexithymia refers to an inability to identify and describe emotions in the self.[4]
Alice in Wonderland experience
Main article: Alice in Wonderland syndrome

In Alice in Wonderland experience, individuals perceive objects (including animals and other humans, or parts of humans, animals, or objects) as appearing substantially smaller than in reality. Generally, the object appears far away or extremely close at the same time. An alternate term for this is somaesthetic aura. Also see § Lilliputian hallucinations
alliteration
Main article: Alliteration

Alliteration is the repetition of initial consonant sounds in neighbouring words.
alogia
Main article: Alogia

Literally, this term means "not having words". The term may refer to either "poverty of speech" or "poverty of thought". In the former, speech, though adequate in verbiage, conveys very little information and may consist of stock phrases or vague references. In poverty of thought, by contrast, there is a far-reaching impoverishment of the entire thinking of the individual, who, as a result, says very little. It is typically a negative symptom of schizophrenia,[1] although it may also be seen in advanced dementia.
amok
Main article: Running amok

The phrase "running amok" describes the behavior of an individual, who is very agitated and can become a danger to others and themself.[5][6] The syndrome of "Amok" is found in the DSM-IV TR.[7]
anhedonia
Main article: Anhedonia

Anhedonia refers to an inability to experience pleasure, and may be described as a feeling of emotional emptiness.[1] It can be a negative symptom of schizophrenia.[1] It also may be seen in severe depressive states and schizoid personality disorder.
anosognosia
Main article: Anosognosia

Anosognosia is a condition in which a person who suffers certain disability seems unaware of the existence of their disability. § Hemiasomatognosia is a subtype of anosognosia in which the person suffering from hemiplegia neglects one half of their body.
Anton's syndrome
Main article: Anton-Babinski syndrome

Anton syndrome, occasionally known as Anton-Babinski syndrome, is a form of cortical blindness in which the individual denies the visual impairment. The individual may attempt to walk, bumping into objects and injuring himself. Anton syndrome is caused by damaging the occipital lobes bilaterally or from disrupting the pathway from the primary visual cortex into the visual association cortex.
anwesenheit

Anwesenheit refers to the feeling of presence of something or some person. It can be seen in normal grief reaction, schizophrenia and some emotionally arousing situations.
apophanous perception

This is an alternate term for delusional perception. It is one of the Schneiderian first rank symptoms and is defined as a true perception, to which an individual attributes a false meaning.
aphemia

Aphemia is the alternate term for mutism. Mutism is absence of speech with apparently normal level of consciousness. Mutism can be dissociative (hysterical) in which an individual (commonly a child or adolescent) stops speaking at once without involvement of any neurological or physical contributing factor; or it can be elective (selective) in which a child does not speak at all in certain situations (such as in school) but speaks well in other conditions (like at home or at play). A rare cause of mutism is akinetic mutism which results due to a lesion around the third ventricle of the brain.
apperception

Apperception is a normal phenomenon and refers to the ability to understand sensory inputs in their context, to interpret them and to incorporate them into experience. Failure of apperception is seen in delirious states.
astasia-abasia
Main article: Astasia-abasia

Astasia-abasia is a form of psychogenic gait disturbance in which gait becomes impaired in the absence of any neurological or physical pathology. The person usually walks in a bizarre manner. They stagger and appear as if going to fall, but always manage to catch hold of something in time. Sometimes these people cannot even stand, but on the other hand they are well able to move their legs while lying down or sitting. Often associated with conversion disorder or somatization disorder.
asyndesis

Asyndesis means loosening of association. A milder form of derailment of thought, it is marked by the individual leaping from topic to topic which have only the most tenuous, if any, connection with each other. This is in contrast with flight of ideas, whereby the individual's successive ideas may be linked and "understandable" to the listener. See also § Akataphasia and § Entgleisen term introduced by (Cameron).
autism
Main article: autism

From aut ="self" and -ism = "state or orientation". Originally, Eugen Bleuler used this term to describe schizophrenia. In general, it refers to any (pathological) tendency to be self-absorbed to such a degree that the feelings, thoughts and desires of a person are governed by their internal apprehension of the world and not by an external reality shared with others.

Today the term is used most often to refer to a specific developmental syndrome (see autism spectrum).[8]:p. 76
autistic thinking

Autistic thinking means thinking not in accordance with consensus reality that emphasizes preoccupation with inner experience. See also § Dereistic thinking. More generally, it means thinking that is guided by internal wishes and desires regardless of external real-world factors.[8]:p. 76
autochthonous delusion
Main article: Delusional intuition

Jaspers defined this as a delusion arising without apparent cause. For example, suddenly, without apparent cause, having the delusional belief that one is an alien.
autokabalesis
Main article: Autokabalesis

Autokabalesis is a term for committing suicide by jumping from a very high place.[9]
automatic obedience

Automatic obedience is an exaggerated co-operation with an examiner's request, as if the individual were an "automaton" robotically obeying a command. It is often a sign of catatonia.
automatism
Main article: Automatism (medicine)

Automatisms are sequences of activity that occur without conscious control. They may be simple and repetitive (tic-like) or complex, and are usually natural-looking but purposeless. Automatic behavior is not usually recalled afterwards.
autoscopy

Autoscopy is the reduplicative hallucination of "seeing one's own body at a distance" and the person sees it from the place where they are located. Autoscopy is sometimes used synonymously with out-of-body experience.
avolition
Main article: Avolition

Avolition is an inability to initiate and complete goal-directed behavior.[1] It can sometimes be misinterpreted as laziness, but it is actually a negative symptom of schizophrenia.
B
Belle indifference

Belle indifference or la belle indifférence is characterized by a lack of concern or feeling of indifference about a disability or symptom.[1] It can be seen in conversion disorder.
bouffée délirante

Bouffée délirante is a French term used in the past for acute and transient psychotic disorders (F23 in ICD-10). In DSM-IV, it is described as "brief psychotic disorder" (298.8). The symptoms usually have an acute onset and reach their peak within two weeks. The symptoms start resolving in a few weeks and complete recovery usually occurs within two or three months.[10]
brain fag syndrome
Main article: Brain fag syndrome

Brain fag syndrome[11] is an example of a culture-bound syndrome. "Brain fag" was once a common term for mental exhaustion. Today, the syndrome describes students (predominantly males, particularly in West Africa) experiencing symptoms including somatic, sleep-related and cognitive complaints, head and neck pains, difficulty in concentrating and retaining information, and eye pain.
brain fog

Synonym of § Clouding of consciousness.
bruxism
Main article: Bruxism

Bruxism refers to teeth grinding behavior that is usually seen in children.
C
Capgras' syndrome or illusion des sosies
Main article: Capgras syndrome

In Capgras syndrome, the individual feels that a person familiar to them, usually a family member, has been replaced by an imposter.[1] This is a type of delusion that can be experienced as part of schizophrenia. Capgras syndrome and several other related disorders are referred to as "delusional misidentification syndrome".
catalepsy
Main article: Catalepsy

Catalepsy is the term for catatonic rigidity of the limbs which often results in abnormal posturing for long intervals.
cataplexy
Main article: Cataplexy

Cataplexy involves a sudden loss of muscle tone, and is generally precipitated by a sudden emotional response.[1]
catatonia
Main article: Catatonia

Catatonia involves a significant psychomotor disturbance, which can occur as catalepsy, stupor, excessive purposeless motor activity, extreme negativism (seemingly motiveless resistance to movement), mutism, echolalia (imitating speech), or echopraxia (imitating movements).[1] There is a catatonic subtype of schizophrenia.[1]
cerea flexibilitas
Main article: Cerea flexibilitas

Cerea flexibilitas, meaning "waxy flexibility", refers to people allowing themselves to be placed in postures by others, and then maintaining those postures for long periods even if they are obviously uncomfortable.[1] It is characterized by an individual's movements having the feeling of a plastic resistance, as if the person were made of wax. This occurs in catatonic schizophrenia, and a person suffering from this condition can have their limbs placed in fixed positions as if the person were in fact made from wax.
chorea
Main article: Chorea (disease)

Chorea is manifest by abnormal involuntary movements. The term comes from Greek word "choreia" as meaning dance, since large groups of muscles are usually involved, which leads to writhing dance-like movements.
circumstantial speech
Main article: Circumstantial speech

Circumstantial thinking, or circumstantial speech, refers to a person being unable to answer a question without giving excessive, unnecessary detail.[12] This differs from tangential thinking, in that the person does eventually return to the original point, circling back on-topic.
clang association
Main article: Clang association

Clang associations are ideas that are related only by similar or rhyming sounds rather than actual meaning.[12]
Claparede's paradox

Claparede's paradox refers to retention of non-verbal and implicit memory in sufferers of Korsakoff's syndrome.[13]
clouding of consciousness

Clouding of consciousness, also known as brain fog or mental fog, is a global impairment in higher central nervous functioning. All aspects of cognitive functioning are affected. On mental status examinations it is manifest by disorientation in time, place and person, memory difficulties caused by failure to register and recall, aphasia, and agnosia. Impaired perception functioning leads to illusions and hallucinations often in the visual sensory modality. This then causes agitation and distress and secondary delusions. The term confusion state is sometimes used to mean clouding of consciousness, but is avoided whenever possible because it is ambiguous.
coenestopathic state

An individual in a coenestopathic state has a localized distortion of body awareness.
confabulation
Main article: Confabulation

Confabulation is the confusion of imagination with memory, or the confusion of true memories with false memories.
conversion disorder
Main article: Conversion disorder

Conversion disorder involves the unintentional production of symptoms or deficits affecting motor or sensory function that are not fully explained by a neurological or medical condition.[1] This can manifest as paralysis, for example. It generally involves psychological factors, and symptoms may worsen in the context of situational conflict.[1]
coprolalia
Main article: Coprolalia

Coprolalia is the involuntary utterance of socially inappropriate phrases. It is a phonic tic associated with Tourette syndrome, although less than 15% of persons with Tourette's have coprolalia.
Cotard delusion
Main article: Cotard delusion

Cotard delusion involves the belief that one of the person's own bodily organs has changed in a bizarre way, has ceased functioning, or has disappeared.[1] It is a type of delusion that can be experienced in schizophrenia.[1]
D
defenestration

Defenestration normally means being thrown out of a window. In psychiatry, it refers to voluntarily jumping out of a window, usually in the context of attempted or completed suicide. Also see § autokabalesis.[14]
déjà vu

In déjà vu, a person feels undue familiarity to an event or a person.
déjà pensée

In déjà pensée, a completely new thought sounds familiar to a person and they feel they have thought the same thing before at some time. This feeling can be caused by seizures which occur in certain parts of the temporal lobe and possibly other areas of the brain as well.
dementia praecox
Main article: Dementia praecox

Dementia praecox refers to a chronic, deteriorating psychotic disorder characterized by rapid cognitive disintegration, usually beginning in the late teens or early adulthood.
dementia pugilistica
Main article: Dementia pugilistica

Dementia pugilistica, also called "chronic traumatic encephalopathy", "pugilistic Parkinson's syndrome", "boxer's syndrome", and "punch-drunk syndrome", is a neurological disorder which affects career boxers and others who receive multiple dazing blows to the head. The condition develops over a period of years, with the average time of onset being about 16 years after the start of a career in boxing.
derailment
Main article: Derailment (thought disorder)

Derailment, also known as loosening of associations, refers to disorganized thinking that jumps between ideas that seem entirely unrelated. Compare § akataphasia, § asyndesis, § entgleisen, § flight of ideas, § knight's move thinking, and § logorrhoea.[12] It can be seen in individuals with schizophrenia, as well as those experiencing mania.[1]
dereistic thinking
Main article: Dereistic thinking

Dereistic means: away from reality, undirected fantasy thinking.[15] Carl Jung wrote, "This is the basic activity of psychic life, this fantasy making", and he used the term image not from afterimage, something one has experienced or seen, but says he takes it from poetic usage.[16] Dereistic thinking: An old descriptive term used to refer to thinking not in accordance with the facts of reality and experience and following illogical, idiosyncratic reasoning. This term is also used interchangeably with § autistic thinking though they are not exact synonyms: dereistic emphasizes disconnection from reality and autistic emphasizes preoccupation with inner experience.
dermatozoenwahn

Alternate term for organic hallucinosis and delusional parasitosis, the continuous belief that one's skin or body has been infested by parasites or insects. This state cannot be diagnosed if the hallucinatory state is produced while the individual is under the influence of drugs or alcohol, or if the individual fulfills the criterion for delirium. In general, if an individual is under the influence of a drug, or experiencing the symptoms of withdrawal from that drug, this condition is not psychiatric but medical, and termed formication.
dhat
Main article: Dhat syndrome

In dhat syndrome there is a complaint of premature ejaculation or impotence and a belief that semen is being passed in the urine.
doppelgänger
Main article: Doppelgänger

The doppelgänger is a phenomenon in which the person feels that their exact "double" is present alongside them all the time and goes with them wherever they go.
E
écho de la pensée

In écho de la pensée, meaning "thought echo" in French, thoughts seem to be spoken aloud just after being produced. The individual hears the "echo" of their thoughts in the form of a voice after they have made the thought. See also § gedankenlautwerden and § thought sonorization.
entgleisen

Literally means jumping off the rails.[dubious – discuss] Alternate term used for derailment of thought (a morbid form of loosening of association or asyndesis). A Schneiderian term by origin. In this form of thought the individual jumps from one topic to another during conversation and both topics have literally no connection with each other. This is in contrast with flight of ideas where connection is present between one topic and another. Compare § akataphasia, § asyndesis, and § derailment.
extracampine

Extracampine hallucinations are hallucinations beyond the possible sensory field, e.g., and individual "seeing" somebody standing behind them is a visual extracampine hallucination experience.[17][18][19]
F
fantasy
Main article: Fantasy (psychology)

Fantasy is imagining that expresses desires and aims.
fatuous affect

The moods of an individual with fatuous affect resemble the moods of a child. This condition is seen in hebephrenic schizophrenia.
flight of ideas

"Flight of ideas" describes excessive speech at a rapid rate that involves causal association between ideas. Links between ideas may involve usage of puns or rhymes.[12][20] It is typical of mania, classically seen in bipolar disorder.[12] Compare § derailment.


folie à deux
Main article: Folie à deux

Also called "induced psychosis", folie à deux is a delusional disorder shared by two or more people who are closely related emotionally. One has real psychosis while the symptoms of psychosis are induced in the other or others due to close attachment to the one with psychosis. Separation usually results in symptomatic improvement in the one who is not psychotic.

Folie communiquée, folie imposée, folie induite, and folie simultanée are the four subtypes of folie à deux.

folie communiquée

Folie communiquée, or subtype C of folie à deux, occurs when a normal person suffers a contagion of their ideas after resisting them for a long time. Once they acquire these beliefs they maintain them despite separation.

folie imposée

Folie imposée, or subtype A of folie a deux, is the most common form in which the dominant person imposes a delusion into a person who was not previously mentally ill. Separation of the two results in improvement of the non-dominant person.

folie induite

In folie induite, or subtype D of folie a deux, a person who is already psychotic adds the delusions of a closely associated person to their own.

folie simultanée

In folie simultanée, or subtype B of folie a deux, a delusional system emerges simultaneously and independently in two closely related persons, and the separation of the two would not be beneficial in the resolution of psychopathology.
Fregoli delusion
Main article: Fregoli delusion

In Fregoli delusion, a person has a delusional belief that various different people are in fact a certain other person, even if there is no physical resemblance.[1]

Fregoli syndrome is considered a form of delusional misidentification "in which the false identification of familiar people occurs in strangers".[21]
G
gedankenlautwerden

In Gedankenlautwerden, an individual hears thoughts spoken aloud. Thoughts are heard in the form of a voice at the same time as they are thought, not afterwards. See also § Écho de la pensée and § Thought sonorization
gegenhalten

Gegenhalten is a catatonic phenomenon in which the subject opposes all passive movements with the same degree of force as applied by the examiner. It is slightly different from § negativism in which the subject does exactly the opposite to what is asked in addition to showing resistance.
H
hemiasomatognosia

Hemiasomatognosia is a subtype of anosognosia in which the person suffering from hemiplegia neglects one half of their body.
hyposchemazia; aschemazia

Hyposchemazia is characterized by the reduced awareness of one's body image and aschemazia by the absence of it. These disorders can have many varied causes such as physical injuries, mental disorders, or mental or physical states. These include transection of the spinal cord, parietal lobe lesions (e.g. right middle cerebral artery thrombosis), anxiety, depersonalization, epileptic auras, migraines, sensory deprivation, and vertigo (i.e. "floating on air").
I
idée fixe

Idée fixe is an alternate term for an overvalued idea. In this condition, a belief that might seem reasonable both to the individual and to other people comes to dominate completely the individual's thinking and life.
ideas of alienation

Thoughts that one's own body part or action is not of one's own.
ideas of influence

Thoughts that one's own action is caused by someone else's will or some other external cause.
ideas of reference
Main article: Ideas of reference and delusions of reference

Ideas of reference are a delusional belief that general events are personally directed at oneself.[12]
illusion

An illusion is a false perception of a detectable stimulus.[1]
J
jargon aphasia

Jargon aphasia is characterized by incoherent, meaningless speech with neologisms (newly invented words). These are unconscious thoughts that find expression when one is off one's guard and must be consciously repressed.
K
Klüver–Bucy syndrome
Main article: Klüver–Bucy syndrome

In Klüver–Bucy syndrome, an individual will display placidity, hyperorality, hypersexuality, and hyperphagia. This condition results from bilateral destruction of the amygdaloid bodies of the limbic system.
knight's move thinking

Knight's move thinking is a complete loosening of associations where there is no logical link between one idea and the next. Based on a knight on a chessboard where the movement can be any L shaped direction, making it difficult to track. Compare § derailment.[22][citation needed]
koro
Main article: Koro (medicine)

Koro is a culture-specific syndrome, generally seen only among Chinese people. It involves a panicked feeling that one's genitals are retracting into the abdomen, and that this will result in death.[1]
kuru
Main article: Kuru (disease)

Kuru (also known as "laughing sickness" due to the outbursts of laughter that mark its second phase) was first noted in New Guinea in the early 1900s. Kuru is now known to be a prion disease, one of several known transmissible spongiform encephalopathies.
L
latah

Latah is a culture-specific syndrome usually seen in Southeast Asia and involves startle-induced disorganization, hypersuggestibility, automatic obedience, and echopraxia (a tendency to mimic examiner's or other person's actions). It is usually associated with women. There is controversy over whether Latah is a real psychiatric condition, or merely a display of exhibitionism that would otherwise not be socially acceptable.
l'homme qui rit

In l'homme qui rit (from the French, meaning "the man who laughs"), an individual displays inappropriate laughter accompanied by release phenomena of the frontal subdominant lobe.
Lilliputian hallucinations
Main article: Alice in Wonderland syndrome

Lilliputian hallucinations are characterized by abnormal perception of objects as being shrunken in size but normal in detail. Usually seen in delirium tremens.
logoclonia

In logoclonia, the individual often repeats the last syllable of a word. Compare echolalia. Often a symptom of Alzheimers or Parkinson's disease.
logorrhoea

Logorrhoea, also known as "volubility", is characterized by fluent and rambling speech using numerous words. Compare § derailment.
M
mania
Main article: Mania

Mania is often mirrored as a minor image of depression. Mania is a state abnormally elevated arousal, affected, and energy level. As mania intensifies, irritability can be more pronounced and result in anxiety or violence. Mania symptoms are elevated mood, flights of ideas, pressure of speech, increased energy, decreased need, desire sleep, and hyperactivity.
mania a potu

Mania a potu is an alcohol intoxication state with violent and markedly disinhibited behavior. This condition is different from violent behavior in otherwise normal individuals who are intoxicated.
metonymy

Metonymy is a speech disturbance in which patients, commonly suffering from schizophrenia, use inappropriate words or expressions that are related to the proper ones. Examples include: consume a menu, instead of a meal; lose the piece of string of the conversation, not the thread of the conversation. See also § word approximation.[23][24]
mitgehen

Mitgehen is an extreme form of mitmachen in which very slight pressure leads to movement in any direction, also called the "anglepoise" effect or "anglepoise lamp sign". This movement occurs despite instructions to resist the pressure, as individuals with this condition often experience even slight pressure as forcible grasping and pushing.
mitmachen

In mitmachen, one's body can be put into any posture, despite instructions given to resist. Compare § mitgehen.
moria

Moria is the condition characterized by euphoric behavior, such as frivolity and the inability to act seriously. In addition, there is a lack of foresight and a general indifference. It is found in frontal lobe lesions, often along with § witzelsucht, particularly when the orbital surface is damaged. Recent research has shown its presence in frontotemporal dementia.
N
negativism

Resistance to attempts to move the subject, who then does the opposite of what is asked. Negativism is usually a sign of catatonia, and may progress to (catatonic) rigidity. It is slightly different from § gegenhalten, in which the individual resists movement but does not perform the opposite movement. Also see: oppositional defiance disorder (ODD).
neologism

In a neurological or psychopathological context, neologisms are nonsensical words or phrases whose origins are unrecognizable, and are associated with aphasia or schizophrenia. Incorrectly constructed words whose origins are understandable may also be called neologisms, but are more properly referred as § word approximations.[25][26]
O
omega sign

The omega sign is the occurrence of a fold (like the Greek letter omega, Ω ) in the forehead, above the nose, produced by the excessive action of the corrugator muscle. It is sometimes seen in depression.
oneiroid state

From Greek oneiros as meaning "dream". In an oneiroid state one feels and behaves as though in a dream. Also known as "oneirophrenia" as described by Ladislas J. Meduna.
oneirophrenia

See § oneiroid state or oneirophrenia.
overvalued idea

Overvalued ideas are exaggerated beliefs that a person sustains beyond reasons, but are not as unbelievable and are not as persistently held as delusions.[27][28] Preoccupation with spouse's possible infidelity can be an overvalued idea if no evidence exists to arouse suspicion. Body dysmorphic disorder's obsessive preoccupation that some aspect of one's own appearance is severely flawed is another example of an overvalued idea.[27]
P
palilalia
Main article: Palilalia

Palilalia is characterized by the repetition of a word or phrase; i.e., the subject continues to repeat a word or phrase after once having said. It is a form of § perseveration.
palinacousis

In palinacousis the subject continues to hear a word, a syllable or any sound, even after the withdrawal of stimulus. It is a type of § perseveration.
palinopsia
Main article: Palinopsia

In palinopsia a visual image persists after the stimulus has gone (similar to an afterimage seen after looking into a bright light).
parapraxis
Main article: Freudian slip

A Freudian slip, or parapraxis, is an error in speech, memory or physical action that is believed to be caused by the unconscious mind.
paraprosopia

A delusion in which a person believes they have seen a face transform into a grotesque form – often described as a 'monster', 'vampire', 'werewolf' or similar. This is very rare and most likely to be described by people suffering from schizophrenia.
paraschemazia

Paraschemazia is characterized by a distortion of body image. It can be caused by hallucinogenic drugs such as LSD and mescalin, epileptic auras, and sometimes migraines.
pareidolia
Main article: Pareidolia

In pareidolia a vague or random stimulus is mistakenly perceived as recognizable. Pareidolia is a type of illusion and hence called "pareidolic illusion".
perseveration
Main article: Perseveration

This term refers to uncontrollable repetition of a particular response, such as a word, phrase, or gesture, despite the absence or cessation of the original stimulus.[29] Usually it is seen in organic disorders of brain, head injury, delirium or dementia, however can be seen in schizophrenia as well.
pfropfschizophrenie

This refers to schizophrenia in people with mild learning disabilities.[30]
piblokto
Main article: Piblokto

Piblokto, pibloktoq, or Arctic hysteria, is a condition exclusively appearing in Inuit societies living within the Arctic Circle. Appearing most prevalently in winter, it is considered to be a form of a culture-specific disorder.[31]

Symptoms can include intense "hysteria" (including screaming and uncontrolled wild behavior), depression, coprophagia, and insensitivity to extreme cold.[32] This condition is most often seen in Inuit women.[33]
poverty of ideas

Often associated with schizophrenia, dementia, and severe depression, poverty of ideas is a thought disturbance in which thought spontaneity and productivity are reduced, and are seen in speech that is vague, has many simple or meaningless repetitions, or full of stereotyped phrases.[34]
pseudologia fantastica

Pseudologia fantastica is a condition in which a person grossly exaggerates their symptoms or even tells a lie about their symptoms in order to get medical attention. Seen in malingering and Munchausen syndrome.
psychological pillow

Where the individual holds their head a few centimetres above the bed. No explanation is offered for this. It is a symptom of catatonia and can last for many hours.
psychopathology
Main article: Psychopathology

Psychopathology is a term which refers to either the study of mental illness or mental distress or to the manifestation of behaviours and experiences which may be indicative of mental illness or psychological impairment.
R
rabbit syndrome

Rabbit syndrome is characterized by rapid rhythmic movements of lips so that it resembles a rabbit chewing.[13] It is a type of dystonic reaction.
reduplicative hallucination

In reduplicative hallucinations there is the perception of seeing a double. Particular kinds of reduplicative hallucination include autoscopy, heautoscopy and out-of-body experiences.
reduplicative paramnesia

Reduplicative paramnesia is a delusional misidentification syndrome in which one's surroundings are believed to exist in more than one physical location.
reflex hallucination

Reflex hallucinations occur when true sensory input in one sense leads to production of a hallucination in another sense, e.g. seeing a doctor writing (visual) and then feeling him writing across one's stomach (tactile).
restlessness

Restlessness has two components: akathisia (subjective "inner" restlessness) and psychomotor agitation (an excess of motor activity).
retardation

Mental retardation is a term used when a person has certain limitations in mental functioning and in skills such as communicating, taking care of him or herself, and social skills.

In children these limitations will cause a child to learn and develop more slowly than a typical child. Children with mental retardation may take longer to learn to speak, walk, and take care of their personal needs such as dressing or eating. They are likely to have trouble learning in school. They will learn, but it will take them longer. There may be some things they cannot learn.[35]
left–right disorientation

Left–right disorientation is one of the four cardinal signs of Gerstmann's syndrome.
S
scanning speech

Scanning speech is an ataxic dysarthria in which syllable durations are equalized. It is characteristic of the dysarthria of multiple sclerosis. Together with nystagmus and intention tremor it forms Charcot's triad 1.
schizophasia
Main article: Schizophasia

Schizophasia, commonly referred to as word salad, is confused, and often repetitious, language that is symptomatic of various mental illnesses.[36]
schnauzkrampf

A schnauzkrampf is a grimace resembling pouting sometimes observed in catatonic individuals.
sensitiver beziehungswahn

Sensitiver beziehungswahn, is an alternate term for ideas of reference. In this the person thinks as people are talking about them or observing them or a talk is going on about them on television or radio. Seen in social phobia, depression, delusional disorder and in schizophrenia where they are often present up to a delusional extent.
Stockholm syndrome
Main article: Stockholm syndrome

The Stockholm syndrome is a psychological response sometimes seen in a hostage, in which the hostage exhibits loyalty to the hostage-taker, in spite of the danger (or at least risk) in which the hostage has been placed.[37] Stockholm syndrome is also sometimes discussed in reference to other situations with similar tensions, such as battered person syndrome,[38] child abuse cases, and bride kidnapping.
synaesthesiae

Also spelled synæsthesia, synaesthesia, or synesthesia—plural synesthesiae, from the Greek 'syn- meaning "union" and aesthesis meaning "sensation", it is a neurological phenomenon in which two or more bodily senses are coupled.
T
telegrammatic or telegraphic speech
Main article: Telegraphic speech

In telegraphic speech conjunctions and articles are missed out; meaning is retained and few words are used.
thought blocking
Main article: Thought blocking

Thought blocking, also referred to as thought withdrawal, refers to an abrupt stop in the middle of a train of thought; the individual might or might not be unable to continue the idea.[12] This is type of formal thought disorder that can be seen in schizophrenia.[1]
thought sonorization

A combined term for § Gedankenlautwerden and § Écho de la pensée ("thought echo")
torpor

Torpor in psychopathology is usually taken to mean profound inactivity not caused by reduction in consciousness.
Tourette syndrome

Tourette syndrome (abbreviated as TS or Tourette's) is a common neurodevelopmental disorder that begins in childhood or adolescence. It is characterized by multiple movement (motor) tics and at least one vocal (phonic) tic. Common tics are blinking, coughing, throat clearing, sniffing, and facial movements. These are typically preceded by an unwanted urge or sensation in the affected muscles, can sometimes be suppressed temporarily, and characteristically change in location, strength, and frequency. Tourette's is at the more severe end of a spectrum of tic disorders. The tics often go unnoticed by casual observers.
traumatic bonding

Traumatic bonding occurs as the result of ongoing cycles of abuse in which the intermittent reinforcement of reward and punishment creates powerful emotional bonds that are resistant to change.[39]
trichotillomania

Also known as "hair pulling disorder", trichotillomania (TTM) is an impulse control disorder characterised by a long term urge that results in the pulling out of one's hair. This occurs to such a degree that hair loss can be seen. Efforts to stop pulling hair typically fail. Hair removal may occur anywhere; however, the head and around the eyes are most common. The hair pulling is to such a degree that it results in distress
V
verbigeration

Verbigeration is a verbal stereotypy in which usually one or several sentences or strings of fragmented words are repeated continuously. Sometimes individuals will produce incomprehensible jargon in which stereotypies are embedded. The tone of voice is usually monotonous. This can be produced spontaneously or precipitated by questioning. The term verbigeration was first used in psychiatry by Karl Kahlbaum in 1874, and it referred to a manner of talking which was very fast and incomprehensible. At the time verbigeration was seen as a "disorder of language" and represented a central feature of catatonia. The word is derived from the Latin word verbum (also the source of verbiage), plus the verb gerĕre, to carry on or conduct, from which the Latin verb verbigerāre, to talk or chat, is derived. However, clinically the term verbigeration never achieved popularity and as such has virtually disappeared from psychiatric terminology. Compare Echolalia.[40]
verstimmung

Refers to an ill-humored mood state often accompanied by low mood and depressive symptoms. The people surrounding the individual often feel upset by this condition.
vorbeigehen; vorbeireden

In vorbeigehen or vorbeireden, an individual will answer a question in such a way that it is clear the question was understood, though the answer itself is very obviously wrong. For example: "How many legs does a dog have?" – "Six". This condition occurs in Ganser syndrome and has been observed in prisoners awaiting trial. Vorbeigehen (giving approximate answers) was the original term used by Ganser but Vorbeireden (talking past the point) is the term generally in use (Goldin 1955). This behavior is also seen in people trying to feign psychiatric disorders (hence its association with prisoners).[41]
W
wahneinfall

Wahneinfall is alternate term for autochthonous delusions or delusional intuition. This is one of the types of primary delusions in which a firm belief comes into the individual's mind "out of the blue" or as an intuition, hence called "delusional intuition". Other types of primary delusions include delusional mood (or atmosphere), delusional (apophanous) perception and delusional memories. Care is taken not to impugn an otherwise-rational individual's instinctive aversion or inexpressible sense of or belief about a thing by dismissing it as wahneinfall.
waxy flexibility

Waxy flexibility, also known as § Cerea flexibilitas, is characterized by an individual's movements having the feeling of a plastic resistance, as if the person were made of wax. This occurs in catatonic schizophrenia, and a person suffering from this condition can have their limbs placed in fixed positions as if the person were in fact made from wax.
waxy rigidity

Compare § mitmachen and § waxy flexibility.
Windigo psychosis
Main article: Wendigo

Windigo (also Wendigo, Windago, Windiga, Witiko, and numerous other variants) psychosis is a culture-bound disorder which involves an intense craving for human flesh and the fear that one will turn into a cannibal. This was alleged to have occurred among Algonquian Indian cultures.
witzelsucht

Witzelsucht is a tendency to tell inappropriate jokes and creating excessive facetiousness and inappropriate or pointless humor. It is seen in frontal lobe disorders usually along with § moria. Recent research has shown that it may also be seen in frontotemporal dementia.[42]
word approximation

Usage of words in an unconventional or inappropriate way (as in § metonymy), or usage of new but understandable words that are conventionally constructed, contrasting with § neologisms, which are new words whose origins cannot be understood.[43][44]
word-salad

Word salad (derived from the German Wortsalat) is characterized by confused, and often repetitious, language with no apparent meaning or relationship attached to them. It is often symptomatic of various mental illnesses, such as psychoses, including schizophrenia. Compare § derailment.
würgstimme

Würgstimme refers to speaking in an odd muffled or strangled voice. It is mainly seen in schizophrenia.
Z
zoophilia
Main article: Zoophilia

One of the paraphilias, characterized by marked distress over, or acting on, urges to indulge in sexual activity that involves animals.

 

 

 A

    Actuator, a motor that translates control signals into mechanical movement. The control signals are usually electrical but may, more rarely, be pneumatic or hydraulic. The power supply may likewise be any of these. It is common for electrical control to be used to modulate a high-power pneumatic or hydraulic motor.[3][4]
    Aerobot a robot capable of independent flight on other planets. A type of aerial robot.
    Arduino The current platform of choice for small-scale robotic experimentation and physical computing.
    Artificial intelligence is the intelligence of machines and the branch of computer science that aims to create it.
    Aura (satellite) a robotic spacecraft launched by NASA in 2004 which collects atmospheric data from Earth.[3]
    Automaton, an early self-operating robot, performing exactly the same actions, over and over.
    Autonomous vehicle a vehicle equipped with an autopilot system, which is capable of driving from one point to another without input from a human operator.

B

    Biomimetic. See Bionics.
    Bionics: also known as biomimetics, biognosis, biomimicry, or bionical creativity engineering is the application of biological methods and systems found in nature to the study and design of engineering systems and modern technology.

C

    CAD/CAM (computer-aided design and computer-aided manufacturing): These systems and their data may be integrated into robotic operations.
    Čapek, Karel: Czech author who coined the term 'robot' in his 1921 play, Rossum's Universal Robots.
    Chandra X-ray Observatory: a robotic spacecraft launched by NASA in 1999 to collect astronomical data.[3]


    Cloud robotics: robots empowered with more capacity and intelligence from cloud.
    Combat, robot: a hobby or sport event where two or more robots fight in an arena to disable each other. This has developed from a hobby in the 1990s to several TV series worldwide.
    Cruise missile: a robot-controlled guided missile that carries an explosive payload.
    Cyborg: also known as a cybernetic organism, a being with both biological and artificial (e.g. electronic, mechanical or robotic) parts.

D

    Degrees of freedom - the extent to which a robot can move itself; expressed in terms of Cartesian coordinates (x, y, and z) and angular movements (yaw, pitch, and roll).[3]
    Delta robot - a tripod linkage, used to construct fast-acting manipulators with a wide range of movement.
    Drive Power - The energy source or sources for the robot actuators.[4]

E

    Emergent behaviour, a complicated resultant behaviour that emerges from the repeated operation of simple underlying behaviours.
    Envelope (Space), Maximum The volume of space encompassing the maximum designed movements of all robot parts including the end-effector, workpiece, and attachments.[4]
    Explosive ordnance disposal robot A mobile robot designed to assess whether an object contains explosives; some carry detonators that can be deposited at the object and activated after the robot withdraws.[3]

F

    FIRST.For Inspiration and Recognition of Science and Technology, is an organization founded by inventor Dean Kamen in 1989 in order to develop ways to inspire students in engineering and technology fields.
    Forward chaining a process in which events or received data are considered by an entity to intelligently adapt its behavior.[3]

G

    Gynoid A humanoid robot designed to look like a human female.

H

    Haptic tactile feedback technology using the operator's sense of touch. Also sometimes applied to robot manipulators with their own touch sensitivity.
    Hexapod (platform) A movable platform using six linear actuators. Often used in flight simulators and fairground rides, they also have applications as a robotic manipulator.
    Hexapod (walker) A six-legged walking robot, using a simple insect-like locomotion.
    Human–computer interaction.
    Humanoid A robotic entity designed to resemble a human being in form, function, or both.
    Hydraulics, the control of mechanical force and movement, generated by the application of liquid under pressure. c.f. pneumatics.

I

    Industrial robot A reprogrammable, multifunctional manipulator designed to move material, parts, tools, or specialized devices through variable programmed motions for the performance of a variety of tasks.[4]
    Insect robot A small robot designed to imitate insect behaviors rather than complex human behaviors.[3]

K

    Kalman filter, a mathematical technique to estimate the value of a sensor measurement, from a series of intermittent and noisy values.
    Kinematics, the study of motion, as applied to robots. This includes both the design of linkages to perform motion, their power, control and stability; also their planning, such as choosing a sequence of movements to achieve a broader task.
    Klann linkage, a simple linkage for walking robots.

L

    Linear actuator A form of motor that generates a linear movement directly.

M

    Manipulator or gripper. A robotic 'hand'.
    Mobile robot A self-propelled and self-contained robot that is capable of moving over a mechanically unconstrained course.[4]
    Muting The deactivation of a presence-sensing safeguarding device during a portion of the robot cycle.[4]

P

    Parallel manipulator an articulated robot or manipulator based on a number of kinematic chains, actuators and joints, in parallel. c.f. serial manipulator.
    Pendant Any portable control device that permits an operator to control the robot from within the restricted envelope (space) of the robot.[4]
    Pneumatics, the control of mechanical force and movement, generated by the application of compressed gas. c.f. hydraulics.
    Powered exoskeleton, is a wearable mobile machine that allow for limb movement with increased strength and endurance.
    Prosthetic robots are programmable manipulators or devices for missing human limbs.[4]

R

    Remote manipulator A manipulator under direct human control, often used for work with hazardous materials.
    Robonaut a development project conducted by NASA to create humanoid robots capable of using space tools and working in similar environments to suited astronauts.

S

    Serial manipulator an articulated robot or manipulator with a single series kinematic chain of actuators. c.f. parallel manipulator.
    Service robots are machines that extend human capabilities.[4]
    Servo, a motor that moves to and maintains a set position under command, rather than continuously moving.
    Servomechanism An automatic device that uses error-sensing negative feedback to correct the performance of a mechanism.
    Single Point of Control The ability to operate the robot such that initiation or robot motion from one source of control is possible only from that source and cannot be overridden from another source.[4]
    Slow Speed Control A mode of robot motion control where the velocity of the robot is limited to allow persons sufficient time either to withdraw the hazardous motion or stop the robot.[4]
    Snake robot A robot component resembling a tentacle or elephant's trunk, where many small actuators are used to allow continuous curved motion of a robot component, with many degrees of freedom. This is usually applied to snake-arm robots, which use this as a flexible manipulator. A rarer application is the snakebot, where the entire robot is mobile and snake-like, so as to gain access through narrow spaces.
    Stepper motor
    Stewart platform A movable platform using six linear actuators, hence also known as a Hexapod.
    Subsumption architecture A robot architecture that uses a modular, bottom-up design beginning with the least complex behavioral tasks.
    Surgical robot, a remote manipulator used for keyhole surgery
    Swarm robotics involve large numbers of mostly simple physical robots. Their actions may seek to incorporate emergent behavior observed in social insects (swarm intelligence).
    Synchro

T

    Teach Mode The control state that allows the generation and storage of positional data points effected by moving the robot arm through a path of intended motions.[4]
    Three Laws of Robotics, coined by the science fiction author Isaac Asimov, one of the first serious considerations of the ethics and robopsychological aspects of robotics.
    Tool Center Point (TCP) The origin of the tool coordinate system.[4]

U

    Uncanny valley A hypothesized zone in which humanoid robot behavior and appearance begin to approach that of actual humans, but are still missing vital elements, to the point that these mimicked actions or images cause revulsion.
    Unimate, the first off-the-shelf industrial robot, of 1961.

W

    Waldo, a short story by Robert Heinlein, that gave its name to a popular nickname for remote manipulators.
    Walking robot, a robot capable of locomotion by walking. Owing to the difficulties of balance, two-legged walking robots have so far been rare and most walking robots have used insect-like multilegged walking gaits.

Z

    Zero Moment Point. Zero Moment Point is a concept related with dynamics and control of legged locomotion, e.g., for humanoid robots. It specifies the point with respect to which dynamic reaction force at the contact of the foot with the ground does not produce any moment, i.e. the point where total inertia force equals 0 (zero).
    ZMP. See Zero Moment Point.