# U (disambiguation)

U, or u, is the twenty-first letter of the English alphabet.
U may also refer to:

## Science
### Mathematics

* $\cup$, union (set theory)
* U-set, a set of uniqueness
* U, the unitary group

### Chemistry

* Uranium, symbol U, a chemical element
* u, the Dalton (unit), a unified atomic mass unit to express atomic and molecular masses

### Astronomy

* U, ultraviolet magnitude, in a UBV photometric system
* U, an October 16 through 31 discovery in the provisional designation of a comet
* U (trans-Neptunian object), a possible extremely distant trans-Neptunian object

### Computing

* <u>, a now-deprecated HTML element denoting underlined text
* U, representing 1.75" as the minimal height of a rack unit
* U, representing a 10x10x10cm CubeSat
* U, universal Turing machine

### Biology

* U, abbreviation for uracil
* U, mitochondrial haplogroup U

### Other scientific uses

* U, a common notation for potential energy
* U, the middle of an edge joining a hexagonal and a square face of the Brillouin zone of a face-centered cubic lattice, in solid-state physics
* U, one of the two subcarrier-modulated color-difference channels in the YUV colorspace, in video
* U, the recommended symbol for a system's internal energy, in thermodynamics
* U, units, any of various standard units of biological activity, such as insulin units, enzyme units, or penicillin units
** U, the enzyme unit
** International units, for which the symbol U is sometimes used
* U, the abbreviation for selenocysteine, an uncommon amino acid containing selenium
* u, the alternative abbreviation for the SI prefix "micro-" when the Greek letter mu (μ) is not available
* U or U-value, the symbol for the overall heat transfer coefficient or thermal transmittance

## Transportation

* U Line, also known as the Uijeongbu Line, a light metro line in Seoul
* Transilien Line U, a line of the Paris transport network
* U (Los Angeles Railway), a former streetcar line in Los Angeles
* Yurikamome, an automated guideway line in Tokyo, labeled
* The official West Japan Railway Company service symbol for:
** Sakurai Line.
** Kibi Line.

## Music

* ’u’, the first opera in the Klingon language
* "U" (Kendrick Lamar song), 2015
* "U" (Super Junior song), 2006
* U (Incredible String Band album), 1970
* U (NiziU album), 2021
* U (Tourist album), 2016 album by Tourist
* "U", a song by KNK from Remain
* "U", a song by Pearl Jam on their album Lost Dogs
* "U", a song by Stray Kids on their mixtape Hop
* "U", a song by S.E.S., released in 2002
* "U", an album by The Enid, released in 2019
* "U", a song by Treasure (band), released in 2022

## People

* An honorific used in Burmese names
* An alternative spelling of Woo (Korean surname), including a list of people with that family name
* An alternative spelling of Woo (Korean given name), including a list of people with that given name
* U of Goryeo (1363–1389), king of Goryeo (Korea), often called King Woo

## Places

* U, Federated States of Micronesia
* Ü-Tsang, one of three historical provinces of Tibet
** Ü (region), a particular region of Ü-Tsang

## Language

* /u/, the close back rounded vowel in the International Phonetic Alphabet
* U language, a language spoken by about 40,000 people in the Yunnan Province of China
* U (cuneiform), a cuneiform sign
* U (Cyrillic), a letter of the Cyrillic script
* U (kana), a Japanese syllabary symbol
* U and non-U English, sociolectal varieties of British English
* Ս, glyph for the Armenian letter se
* u, an abbreviation for "you" in computer chats
* U-, a prefix used for German submarines during World War II
* U, a title roughly equal to "Mister" in Burmese
* The Greek letter μ

## Film and television

* U (film), a 2006 French animated feature film directed by Serge Elissalde and Grégoire Solotareff
* The U (film), a 2009 documentary about the Miami Hurricanes football team
* U (Universal), a media content rating used in the following countries:
** United Kingdom, issued by the British Board of Film Classification
** India, issued by the Central Board of Film Certification
** Malaysia, issued by the Film Censorship Board of Malaysia
** France, documented at Censorship in France
** India, Latvia, Malta, Mauritius and Slovakia, documented at Motion picture content rating system and Television content rating system
* U (TV channel), a former television channel in New Zealand
* U, the production code for the 1965 Doctor Who serial The Myth Makers
* The American Spanish-language network Univisión has the U logo
* U (streaming service), (formerly UKTV Play) a free British streaming service owned by UKTV

## Other uses

* University, commonly abbreviated "U"
* U Mobile, Malaysian mobile phone and data service provider
* U-bend, a U-shaped plumbing trap
* U-bolt, a U-shaped metal fastener
* Ⓤ, (U inside a circle), hechsher or kosher certification by the Orthodox Union
* U, =U= or -U-, symbol for Ustaše Croatian movement
* Nickname for football teams:
** La U or Universitario de Deportes, Peru
** Universitatea Cluj, Romania
* U, the color blue in Magic: The Gathering
* Wii U, the sixth Nintendo video game home console, released in 2012
* Uniform, the military time zone code for UTC−08:00
* "U" Is for Undertow, the twenty-first novel in Sue Grafton's "Alphabet" mystery series, published in 2009
* Underscore, originally invoked in HTML using <u>
* U, a brand of menstrual hygiene products by Kotex
* U, the logo for Unilever