# D (disambiguation)

D is the fourth letter of the Latin alphabet.
D or d may also refer to:

## Places

* D River, in Oregon, US
* Detroit, US (nickname "D")

## People with the name

* D, the bass player for Australian band Testeagles
* "D!" or "Dee!", names of Detlef Soost, a German dancer and choreographer
* D, nickname of Indian actor Darshan (Kannada actor)
* D, nickname of Indian actor Dhanush (cf. D50 (film))

## Arts, entertainment, and media
### Fictional entities

* D, a character in a series of novels titled Vampire Hunter D by Hideyuki Kikuchi
* D, a nickname given to Count Dracula in the novel Dracula written by Bram Stoker
* D, one of the characters in Another Code: Two Memories (Trace Memory)
* Count D, a character in the anime/manga series Pet Shop of Horrors
* Substance D, a fictional recreational drug in the novel and film A Scanner Darkly

### Games

* D (video game), a game released in 1995 for the PC, 3DO, PlayStation and Sega Saturn

### Music
#### Groups and labels

* D (band), a Japanese rock/metal band
* D Records, a former record label in Houston, Texas, US
* "d:" or "d:?", often used to refer to the Christian rock band Delirious?
* "The D", one of the names of comedy rock band Tenacious D

#### Albums

* D (Deuter album), 1971
* D (Daryl Hall album), 2024
* D (Os Paralamas do Sucesso album), 1987
* D (White Denim album), 2011
* D (single album), by Big Bang, 2015
* D, followed by a number, a composition by Franz Schubert according to the Schubert Thematic Catalogue
* Substance D, a drum and bass compilation album by Dieselboy

#### Other uses in music

* D (musical note)
** D major, a scale
** D major chord; See Chord names and symbols
** D minor, a scale
* Steinway D-274 or D, a concert grand piano model manufactured by Steinway & Sons
* "D", a song by Little River Band from their album Playing to Win

### Periodicals

* D, a weekly supplement to the Italian newspaper la Repubblica
* D Magazine, a magazine for the city of Dallas, Texas, US

### Other uses in arts, entertainment, and media

* D (film), a 2005 Bollywood film
* Initial D, a 1995 Japanese manga and anime about mountain drifting that has spawned several arcade and console games
* D, the production code for the 1964 Doctor Who serial Marco Polo
* "D" Is for Deadbeat, the fourth novel in Sue Grafton's "Alphabet mystery" series, published in 1987
* The D logo for the Russian television channel Domashny

## Business and economics

* Demand (D), in economics
* Dominion Resources (New York Stock Exchange ticker symbol D)
* Federal Reserve Bank of Cleveland (serial numbers of United States dollars, beginning with D)
* Penny (British pre-decimal coin) (d)

## Computing, technology, and engineering
### Computing

* .d, a file format used for Agilent MassHunter mass spectrometry software
* .d, a pathname component suffix for a directory; for example with the init program
* -d, a suffix of a daemon, a computer program that runs as a background process
* D - Minimal Protection, a security division in the Trusted Computer System Evaluation Criteria

#### Programming languages

* D (programming language), a C++-like programming language developed by Walter Bright
* D, a programming language designed to be used with the DTrace dynamic tracing framework
* Hugh Darwen's Tutorial D, part of a proposed family of database query languages called "D"

### Other uses in technology

* D, Mitsubishi Electric's mobile phones in Japan
* D battery, a standard size dry cell battery in electronics
* d', sensitivity index, a statistic used in signal detection theory

## Linguistics

* ’d, a contraction of the English words had and would
* Dingir ($^D$), the Sumerian sign for deity
* [d] or /d/, Voiced alveolar stop consonant in the International Phonetic Alphabet

## Mathematics and science
### Measurements

* d, deci-, SI prefix factor 0.1

### Astronomy and Earth science

* D, a February 16 through 29 discovery in the provisional designation of a comet or asteroid
* D, for "Degenerate", a white dwarf in stellar classification
* D/, for "destroyed/disappeared" in comet nomenclature
* D region, part of the ionosphere

### Mathematics

* D, 500 in Roman numerals
* D, Thirteen, or D in hexadecimal and other positional numeral systems with a radix of 14 or greater
* D and d, the derivative operators
* d, the symbol for the total differential operator; in a related but more general meaning, it is the exterior derivative operator in differential geometry
* d, often a variable for the diameter of a circle in geometry
* d(n), Divisor function, the number of positive divisors of an integer n
* $\mathbb {D}$ in blackboard bold, the unit disk in the complex plane, or the decimal fractions; see Number
* Cohen's d, a statistical measure of effect size.

### Biology, chemistry, and medicine

* D, Aspartic acid, in biochemistry
** D (or Asp), an abbreviation for the amino acid aspartate
* D, Diarrhea
* D, deuterium, an isotope of hydrogen
** d, Deuteron, the nucleus of deuterium
* $_D$- prefix, a dextrorotatory compound
* ATC code D Dermatologicals, a section of the Anatomical Therapeutic Chemical Classification System
* Haplogroup D (mtDNA), a human mitochondrial DNA (mtDNA) haplogroup
* Haplogroup D-M174, a Y-chromosomal DNA (Y-DNA) haplogroup
* Vitamin D

### Physics

* D, Debye (D), a unit of electrical dipole moment
* D, Dioptre (D), a unit of measurement of the optical power of a lens or curved mirror (also in Medicine)
* D, Diffusion coefficient (D), in molecular physics
* D, Electric displacement field (D)
* D meson, mesons containing charm quarks in particle physics
* d, thickness, diameter, relative density, lattice plane spacing, and degeneracy of vibrational mode, in molecular spectroscopy
* D band (disambiguation)

#### Solid state physics

* Debye–Waller factor (D)
* Diode (D), an electronic component
* $D(E)$, the density of states at energy $E$

## Time

* Day (d), in metrology
* December (D), in calendars
* Dominical letter D, for a common year starting on Thursday

## Transportation

* D (Los Angeles Railway), a line operated by the Los Angeles Railway, US
* D (New York City Subway service), US
* D Line (Los Angeles Metro), US
* Drive, or D, the forward cruising gears in an automatic transmission
* Tesla Model D, a concept all-wheel drive electric sedan
* Line D of the Buenos Aires Subte
* , the official West Japan Railway Company service symbol for the JR West Nara Line.
* Media–Sharon Hill Line, a SEPTA Metro service, labeled D
* The international vehicle registration code for Germany (Deutschland)

## Other uses

* D, a normal modal logic
* D (grade), a below average grade in education
* D, a brassiere cup size
* d, the number of sides of dice in role-playing games
* d, the common US measurement of the penny size (an approximation of length), of a nail
* D-Company, a criminal group
* Daughter (d)
* Defense (sports) (D)
* Democrat (D), a member of the US Democratic Party
* Denarius, a Roman coin
* Died (d.)
* Dominant person (D/), in dominance and submission
* Delta, the military time zone code for UTC+04:00