Do Loop
A programming language statement which allows code to be repeatedly executed.
Dobson Unit
Unit used in geophysics to measure the ozone in the atmosphere.
Dodd Bars
A secondary alignment method. Consists of two bars that are similar in configuration to reverse dial indicator bars.
A polygon with 12 sides.
A solid figure with 12 faces.


A thick, oily liquid of the paraffin series. It is used as a solvent, distillation chaser and is also the average component of diesel fuel.

Dolby Digital
A five-channel system consisting of left, centre, right and left rear, right rear channels. All processing is done in the digital domain.
Dolby Prologic
This is a four-channel sound reproduction system consisting of left, center, right and rear channel, (the single rear channel is usually played through two speakers).
Dolby, Ray
Audio system innovator and founder of Dolby Laboratories.
The set of all allowable inputs for a function.
Domain Name
The unique name that identifies an Internet site.
Domain Naming System
A system used by the Internet for translating names of host computers into addresses.
Domain of the Function
The set of numbers x for which f(x) is defined.
A roof formed by a series of arches, roughly forming a semicircle.
Two congruent squares joined along an edge.
Domoic Acid


Domoic acid is a toxic amino acid produced by certain species of algae.

The principal tower of a castle.
An atom which is likely to give off one or more electrons when placed in a crystal.
Donor Level
The level that donates conduction electrons to the system.
Opening to a room, compartment or system.
The chemical element (impurity) added in small amounts to an otherwise pure semiconductor material to modify the electrical properties of the material.
The intentional alloying of semiconductor materials with controlled concentrations of donor or acceptor impurities
Doppler Effect
A change in the frequency of a periodic wave due to the motion of the observer, the source, or both.
Doppler Sonar
An acoustic instrument that measures the change in the acoustic frequency of the scattered sound or echo from that of the transmitted pulse. The magnitude and direction of the shift in frequency is related to the relative motion of the sensor and the scatterer.
Doric Order
The first and simplest of the three Greek orders and the only one that normally has no base.
Dormant Volcano
The term is used to describe a volcano which is presently inactive but which may erupt again.
Dormer Window
A window housed in a gable or similar structure affixed to the sloping part of a roof, providing natural light and ventilation to the rooms beneath the roof.
Abbreviation of Disk Operating System.
A measure of the energy deposited within a given mass of a patient.
Dose Equivalent
Parameter used to express the risk of the deleterious effects of ionization radiation upon living organisms.
Dose Rate
A measure of the dose delivered per unit time.
A device worn by a worker for determining the worker's accumulated noise exposure with regard to level and time according to a pre-determined integration formula.
A description of a point in which the point has a definite size.
Dot Product
The dot product of two vectors is obtained by adding the products of the respective components of the vectors.
Dots Per Inch
A unit used to measure the resolution, or sharpness of an image.
Double Acoustic Barrier
An acoustic barrier consisting of two panels with a gap between.
Double Blind Experiment
Neither the subjects nor the people evaluating the subjects knows who is in the treatment group and who is in the control group.
Double Bond
When an atom is bonded to another atom by two sets of electron pairs.
Double Data Rate
A fast type of RAM for a PC, originally only used on high performance graphics cards but now being used for general memory in most high-end PCs.
Double Displacement
A reaction in which two reactants trade fragments.
Double Glazing
Two layers of glazing used to improve thermal and acoustic radiation.
Double Helical Gear
The double helical gear gives a much smoother still operation than the spur or helical gear and reduces the noise levels further.
Double Helix
The natural coiled conformation of two complementary, antiparallel DNA chains by the formation of A-T and G-C base pairs.
Double Hung Window
Two sashes which, when both are closed, are positioned one immediately above the other.
Double Integrating Gyro
A single-degree-of-freedom gyro having essentially no restraint of its spin axis about the output axis.
Double Row Bearing
A bearing having two rows of rolling elements.
Double Star
Two stars in nearly the same line of sight and at approximately the same distance from the observer.
Double Word
Unit of information equal to 2 short words, 4 bytes or 32 bits.
Double-Blind Reference Oil
A reference oil, the identity of which is unknown by either the submitting source or the test facility and is not known to be a reference oil by the test facility.
Double-Ended Spanner
A tool which has a hexagon ring at each end.
Double-Tube Shock Absorber
An older design of hydraulic shock absorber using two concentric tubes, one serving as the working cylinder, the other as the reservoir.
Dovetail Joint
A joint where the fingers are shaped like a doves tail, used to join pieces at 90 degrees.
Dovetail Saw
A saw designed for cutting dovetail joints and other wood joints.
A pin fitted or keyed in two adjacent parts to accurately align the parts when assembling them.
Down Feed
A seldom used method of feeding work into milling cutters.
Down Quark
The second flavour of quark (in order of increasing mass), with electric charge -1/3.
Large external pipes in many water-tube boilers, carrying unheated cold water from the steam drum down to the water drum as part of the circulation path.
A device which provides frequency conversion to a lower frequency.
The opposite of aerodynamic lift, sometimes referred to as negative lift. The force caused by the air over the wings to push the car into the ground, increasing grip and cornering speeds.
Downsampling is used to reduce the sampling rate of data.
The vertical part of a drainage system from a roof-which forms a channel or pipe to remove water from the gutters.
Downstream Face
The side of the dam that is not against the water.
Downturned Eye
Refers to the eye of a leaf spring when the spring turns down to form the eye.
Twelve pieces of something.