J, or j, is the tenth letter of the English alphabet. J may also refer to: * Palatal approximant in the International Phonetic Alphabet * J, Je (Cyrillic), Cyrillic letter Je

Astronomy

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

Computing

* J (programming language), successor to APL * J Sharp, 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

) in fields where ''i'' is used for a different purpose (such as electric current) * ''j'' and ''j²'' (or

\bar

) 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 * , an index variable in a matrix (mathematics), matrix * The j-invariant, a modular function

Physics and chemistry

* J, Joule, the SI unit of energy * J, the SI-recommended dimension symbol for luminous intensity, conventionally rendered in a sans-serif typeface * , 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

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 (Jaehyun album), ''J'' (Jaehyun album), album by South Korean singer Jaehyun

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'' * Serial Designation "J", one of the antagonists from the web series ''Murder Drones'' (2021-2024)

Writers

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

Transportation

* J (Los Angeles Railway) * J (New York City Subway service) * J Church, J Church (San Francisco Muni) * J Line (Los Angeles Metro) * NZR J class (1939), 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

, 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

Other uses

* J, slang for joint (cannabis) * J, slang for Air Jordan shoes * J, slang for a glossary of basketball terms#J, 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 Identifying marks on euro coins#Mint marks, 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 (England and Wales), 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), ''J'' (novel), a 2014 novel by Howard Jacobson * ''ʲ'', the symbol for Palatalization_(phonetics), Palatalization in the IPA * Juliet, sometimes used as the unofficial List of military time zones, 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