U, or u, is the twenty-first letter of the English alphabet.

U may also refer to:

Science

Mathematics , 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 HTML element denoting underlined text: see underscore#HTML <u> and CSS 'U' (or sometimes RU) is a standard height unit of measure in rack units, with each U equal to U, universal Turing machine The prefix (then a number) is used to indicate a codepoint as being in the Unicode character encoding system (to distinguish it from other encoding systems). For example, the codepoints for the letters and are given formally as and .

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, representing a 10x10x10cm CubeSat 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 Understeer gradient

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 (Incredible String Band album), 1970 U (NiziU album), 2021 U (Tourist album), 2016 album by Tourist U (Underscores album), 2026 "U" (Super Junior song), 2006 "U", a song by Kendrick Lamar from To Pimp a Butterfly "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, 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, i.e. "upper-class" U (Armenian letter) (ՈՒ, ու), an Armenian diagraph 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 episodes 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, the production code for the 1965 Doctor Who serial The Myth Makers

Media 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 Channel U (Singaporean TV channel), a Singaporean Chinese-language television channel 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

See also The U (disambiguation) U class (disambiguation) You (disambiguation) Yoo (disambiguation) Yu (disambiguation) Yew (disambiguation)