From QRZ.Com, the Icom handout, and Part 97 Of The FCC Rules -
Ham Radio Glossary - An overview of amateur radio terms.

Data communications
Transfer of data between two or more locations.

dBd
Unit of RF power as compared to a dipole antenna.

dBi
Unit of RF power as compared to an isotropic antenna.

dBm
Decibels measure, 1 mW with a load impedance of 600 ohms
(0 dBm=1 mW).

DC
Direct Current

DC ground
A connection point directly to chassis or battery ground to prevent
build-up of hazardous DC voltages.

DCS
Digital Coded Squelch

DE
Telegraphy for "from", such as "DE N5VLZ".

Deviation
The resultant frequency swing of a signal that is frequency modulated (FM).
It is a measurement for an FM signal for the maximum carrier frequency
changes either side of the carrier frequency.

Dielectric
A non-conductive material used to separate the center conductor and shield (conductor) in coaxial cable; typically made of foam or plastic.

Dipole
Likely the most common wire antenna amongst hams, the easy-to-homebrew
dipole consists of two legs (each 1/4 wavelength) which typically extend horizontally and away from each other. One leg connects to the coax's
center conductor, and the other leg connects to the coax's shield as a counterpoise. The dipole antenna is usually strung in a horizontal fashion between trees, and works best when at least 1/4 wavelength above the earth.

Distress call
Signals a life-threatening situation, or one involving the safety of life, and/or the protection of property, such as severe weather (tornadoes, hurricanes, flooding, etc.). Most commonly referred to as an SOS or MAYDAY call. Also known as emergency or priority traffic.

Distress frequency
A frequency or channel specific to use in distress calling.
Radiotelephne distress frequencies are 2.182 Mhz and 156.8 Mhz.
Survival craft use 243 Mhz. Maritime distress frequencies are the
same, while aviation frequencies are 121.5 Mhz.

Downlink
Frequency that a repeater or satellite transmits on to a user.
Also see Uplink.

DR
A CW abbreviation for "dear", used as a respectful salutation. Example
"GOOD EVENING, DR JOHN, HW ARE U?"

Driven Element
An "arm" of a yagi antenna to which RF power is fed from the coax.

DSP
Digital Signal Processor. Used to improve the signal to noise ratio
for clearer and more legible communications. Relatively new to the
ham radio.

DSSB
Double Suppressed Sideband modulation

DSW
Russian abbreviation for "goodbye" on CW.

DTCS
Digital Tone Coded Squelch. A selective call system.

DTMF
"Dual Tone, Multiple Frequency"; a tone that is actually comprised of two different tones sounded at the same time. It is what you hear when you use
the pushbuttons on a standard non-pulse telephone in the U.S. It is also
a common way to send analog numeric information, since each numeral between
0 and 9 has its own separate tone (and also # and *, and in the case of
some radios, A, B, C, and D). These are also used to send remote radio or repeater control commands, such as for net announcements, temporary
disabling of the 3 minute timeout timer (such as during ARRL Audio News
and/or Amateur Radio Newsline) during traffic nets, etc.

Dualwatch
Receiving two signals simultaneously.

Dummy Load
Typically a power dissipating resistor or device substituted in place of an antenna on a transmitter, used for testing purposes. It's usually a non-radiating 50 ohm load.

Duplex
An operation mode in which the transmit and recive frequencies are
different.

Duplexer
A device which divides transmit and receive frequencies.

Duty cycle
The ratios of transmit to receive time.

DX
Long distance; making contacts over long distances. For HF contacts, "DX"
is typically considered as such if the station contacted is outside of your country. In some other cases, making a contact over what is considered extremely long distances (for the conditions and band) can be considered
"DX" (i.e., a QSO from one end of a state to another, on 2 meters simplex,
can be considered "'DX").

DXCC
"DX Century Club"
An ARRL-sponsored club by which membership is allowed only after showing
proof of having made contact with at least 100 different countries.
For more information, please see http://www.arrl.org.

DXpedition
Derived from the words "DX" and "expedition", this term typically refers to
a trip made by experienced ham operator(s) to a "DX" country for the
purpose of providing other hams an opportunity to make a contact (QSO) into that country.
--- SBBSecho 3.20-Win32
* Origin: The Thunderbolt BBS - Little Rock, Arkansas (1:2320/33)