D is the fourth letter of the Latin alphabet.
D or d may also refer to:
Places
People with the name
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 ' (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
Other uses in music
Periodicals
- D la Repubblica, stylized as a lower-case 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
Computing, technology, and engineering
Computing
- .d, a file format used for Agilent MassHunter mass spectrometry software
- , 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
Linguistics
- âÂÂd, a contraction of the English words had and would
- Dingir (<sup>D</sup>), the Sumerian sign for deity
- <nowiki>[d] or /d/</nowiki>, Voiced alveolar stop consonant in the International Phonetic Alphabet
Mathematics and science
Measurements
- d, deci-, SI prefix factor 0.1
Astronomy and Earth science
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
- 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
- <sub>D</sub>- 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
Time
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
- MediaâÂÂSharon Hill Line, a SEPTA Metro service, labeled D
- The international vehicle registration code for Germany ()
- Bandung and Cimahi (vehicle registration prefix D)
- Germany (aircraft registration prefix D)
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
See also