J (disambiguation)

J, or j, is the tenth letter of the English alphabet.

J may also refer to:
 * Palatal approximant in the International Phonetic Alphabet
 * J, Cyrillic letter Je

Astronomy

 * J, a provisional designation prefix for some objects discovered between May 1 and 15 of a year

Computing

 * J (programming language), successor to APL
 * J# programming language for the Microsoft .NET Framework
 * J operator, a programming construct
 * J (operating system), an operating system for ICL's System 4 series of computers

Genetics and medicine

 * Haplogroup J (mtDNA)
 * Haplogroup J (Y-DNA)
 * ATC code J Antiinfectives for systemic use, a section of the Anatomical Therapeutic Chemical Classification System

Mathematics

 * J, symbol used to denote the Bessel function
 * j, used as the symbol for the imaginary unit ($$\sqrt{-1}$$) in fields where i is used for a different purpose (such as electric current)
 * j and j2 (or $$\bar{j}$$) are also used for the complex cube roots of unity
 * j, a number with the property j 2 = +1, used in the definition of the split-complex numbers
 * j, the second imaginary unit of a quaternion
 * $j$, an index variable in a matrix
 * The j-invariant, a modular function

Physics

 * J, Joule, the SI unit of energy
 * J, the SI-recommended dimension symbol for luminous intensity, conventionally rendered in a sans-serif typeface
 * $j$, current density
 * second moment of area
 * J, name given by Samuel C. C. Ting for the J/ψ particle
 * J-coupling, indirect dipole-dipole coupling between two nuclear spins

Music

 * J, stage name of Jang Ye-eun, a member of the K-Pop group STAYC
 * J (Korean singer), a Korean pop singer
 * J (musician), a Japanese rock musician
 * J., nickname of American White Zombie guitarist Jay Yuenger
 * J., stage name of German musician Jaye Muller
 * J Mascis, American singer and guitarist of Dinosaur Jr.
 * J Records, a record label

Albums

 * J, album by Lazza List of number-one hits of 2020 (Italy)

Songs

 * "J", song by Reggie and the Full Effect from the album Last Stop: Crappy Town
 * "J", song by Mindless Self Indulgence from the album Frankenstein Girls Will Seem Strangely Sexy

Film and television

 * Agent J, a character in the Men in Black films portrayed by Will Smith
 * J, an antagonist in Bobobo
 * Kamen Rider J, a Japanese movie
 * J, the production code for the 1964 Doctor Who serial Planet of Giants

Writers

 * J (sometimes given as I), pen name of the Danish novelist Cornelia von Levetzow (1836–1921)

Transport

 * J (Los Angeles Railway)
 * J (New York City Subway service)
 * J Church (San Francisco Muni)
 * J Line (Los Angeles Metro)
 * NZR J Class, a 4-8-2 type class of steam locomotive used by New Zealand Railways
 * Transilien Line J, a line of the Paris transport network
 * JRW kinki-J.svg, the official West Japan Railway Company service symbol for the Bantan Line.

Other uses

 * J, slang for joint (cannabis)
 * J, slang for Air Jordan shoes
 * J, slang for a jump shot in basketball
 * J band (disambiguation)
 * J (psychedelic), an entactogenic drug
 * Elgin, Joliet and Eastern Railway, a Chicago railway sometimes referred to as "The J"
 * J, the international license plate code for Japan
 * J, the Canadian postal code for the western and northern regions of Quebec
 * J, German mint mark for the city of Hamburg
 * J abbreviation for Jahwist, one of the hypothesized major authors of the Torah
 * J, an abbreviated title of a High Court judge (in Law Reports, etc.), e.g. Bloggs J
 * J. The Jewish News of Northern California, a weekly newspaper serving the Jewish community in Northern California
 * J, the narrator of Jerome K. Jerome's novel Three Men in a Boat
 * J., Jezper Söderlund, the trance artist
 * Lamborghini Aventador J, a 2012 Lamborghini supercar
 * J (novel), a 2014 novel by Howard Jacobson
 * ʲ, the symbol for Palatalization in the IPA
 * Juliet, sometimes used as the unofficial military time zone code for local time
 * "J" Is for Judgment, the tenth novel in Sue Grafton's "Alphabet mystery" series, published in 1993
 * Guy Big J, range of trucks produced by Guy Motors of England between 1964 and 1978
 * [J], code for academic journal in the reference section of an academic work