A diffuser-augmented wind turbine is a wind turbine modified with a cone-shaped wind diffuser that is used to increase the efficiency of converting wind power to electrical power.

Diffusion is the net movement of anything from a region of higher concentration to a region of lower concentration.

Referring to data in numerical form.

A display in which the measured quantity is given in digital form.

A technique using digital codes. It enables a radio station to establish contact with, and transfer information to, other stations complying with the relevant recommendations of the International Radio Consultative Committee (CCIR).

A digital voltmeter measures an unknown input voltage by converting the voltage to a digital value and then displays the voltage in numeric form.

Digitization is the process of converting information into a digital (i.e. computer-readable) format.

An electronic power component which allows for a flow of current in one direction only; from anode to cathode.

The common allotrope of elemental oxygen on Earth, O2, is generally known as oxygen, but may be called dioxygen, diatomic oxygen, molecular oxygen, or oxygen gas to distinguish it from the element itself and from the triatomic allotrope ozone, O3.

Electrical current that flows in one direction only.

This is electrical current that does not alternate, the electrons flow through the circuit in one direction.

A propulsion system arrangement where the engine is directly coupled to the shaftline. It is usually applied on low-speed engines.

A wind turbine whereby the rotor is directly connected to the generator.

A heat pump system in which the refrigerant is circulated in pipes buried underground.

A refrigeration system in which the refrigerant expansion occurs due to the direct absorption of heat from the primary medium to be cooled.

Direct insolation is the solar insolation measured at a given location on Earth with a surface element perpendicular to the Sun's rays, excluding diffuse insolation (the solar radiation that is scattered or reflected by atmospheric components in the sky).

A direct plasmonic solar cell is a solar cell that converts light into electricity using plasmons as the active, photovoltaic material.

The method used for reduction of NOx emissions by the injection of water directly into the combustion chamber via a separate nozzle: 50-60% NOx reduction with some fuel consumption penalty.

Direct-buried cable (DBC) is a kind of communications or transmissions electrical cable which is especially designed to be buried under the ground without any kind of extra covering, sheathing, or piping to protect it.

When viewed from astern, if the propeller revolves in a clockwise direction when going ahead, it is known as right-handed. If in an anticlockwise direction, it is left-handed.