J (disambiguation)

Last updated September 16, 2025

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

Astronomy

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

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

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

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 j² = +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

J, Joule, the SI unit of energy
J, the SI-recommended dimension symbol for luminous intensity, conventionally rendered in a sans-serif typeface
$j \to$ , 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
J (element), atomic symbol of Jod, German for iodine

"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

Agent J, a character in the Men in Black films portrayed by Will Smith
Canal J, a French children's television channel
J, an antagonist in Bobobo
Kamen Rider J , a Japanese movie
J, the production code for the 1964 Doctor Who serial Planet of Giants
Serial Designation "J", one of the antagonists from the web series Murder Drones (2021-2024)

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

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
, the official West Japan Railway Company service symbol for the Bantan Line
Saviem J, also known as the Renault J, a range of medium-duty trucks
"The J", a nickname for the Elgin, Joliet and Eastern Railway, a former railroad

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