U is the twenty-first letter of the Latin alphabet. U may also refer to:

Science

Mathematics

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union (set theory) In set theory, the union (denoted by ∪) of a collection of sets is the set of all elements in the collection. It is one of the fundamental operations through which sets can be combined and related to each other. A refers to a union of ze ...

* U-set, a

set of uniqueness In mathematics, a set of uniqueness is a concept relevant to trigonometric expansions which are not necessarily Fourier series. Their study is a relatively pure branch of harmonic analysis. Definition A subset ''E'' of the circle is called a set ...

* U, the

unitary group In mathematics, the unitary group of degree ''n'', denoted U(''n''), is the group of unitary matrices, with the group operation of matrix multiplication. The unitary group is a subgroup of the general linear group . Hyperorthogonal group is ...

Chemistry

Uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

, symbol U, a chemical element * u, the

Dalton (unit) The dalton or unified atomic mass unit (symbols: Da or u) is a non-SI unit of mass widely used in physics and chemistry. It is defined as of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at ...

, a unified atomic mass unit to express atomic and molecular masses

Astronomy

* U, ultraviolet magnitude, in a

UBV photometric system The UBV photometric system (from ''Ultraviolet, Blue, Visual''), also called the Johnson system (or Johnson-Morgan system), is a photometric system usually employed for classifying stars according to their colors. It was the first standardized ...

* U, an October 16 through 31 discovery in the provisional designation of a

comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...

* U (TNO), a possible extremely distant trans-Neptunian object

Computing

* , 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 A CubeSat is a class of miniaturized satellite based around a form factor consisting of cubes. CubeSats have a mass of no more than per unit, and often use commercial off-the-shelf (COTS) components for their electronics and structure. CubeSats ...

* U,

universal Turing machine In computer science, a universal Turing machine (UTM) is a Turing machine that can simulate an arbitrary Turing machine on arbitrary input. The universal machine essentially achieves this by reading both the description of the machine to be simu ...

Biology

* U, abbreviation for

uracil Uracil () (symbol U or Ura) is one of the four nucleobases in the nucleic acid RNA. The others are adenine (A), cytosine (C), and guanine (G). In RNA, uracil binds to adenine via two hydrogen bonds. In DNA, the uracil nucleobase is replaced b ...

* 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 In mathematics and solid state physics, the first Brillouin zone is a uniquely defined primitive cell in reciprocal space. In the same way the Bravais lattice is divided up into Wigner–Seitz cells in the real lattice, the reciprocal lattice ...

of a face-centered cubic lattice, in solid-state physics * U, one of the two subcarrier-modulated color-difference channels in the

YUV YUV is a color model typically used as part of a color image pipeline. It encodes a color image or video taking human perception into account, allowing reduced bandwidth for chrominance components, compared to a "direct" RGB-representation. H ...

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 The enzyme unit, or international unit for enzyme (symbol U, sometimes also IU) is a unit of enzyme's catalytic activity. 1 U (μmol/min) is defined as the amount of the enzyme that catalyzes the conversion of one micromole of substrate per min ...

International unit In pharmacology, the international unit (IU) is a unit of measurement for the effect, not mass of a substance; the variance is based on the biological activity or effect, for the purpose of easier comparison across similar ''forms'' of substan ...

s, 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- ''Micro'' (Greek letter μ ( U+03BC) or the legacy symbol µ (U+00B5)) is a unit prefix in the metric system denoting a factor of 10−6 (one millionth). Confirmed in 1960, the prefix comes from the Greek ('), meaning "small". The symbol for ...

" when the Greek letter mu (µ) is not available * U or U-value, the symbol for the overall heat transfer coefficient or

thermal transmittance Thermal transmittance is the rate of transfer of heat through matter. The thermal transmittance of a material (such as insulation or concrete) or an assembly (such as a wall or window) is expressed as a U-value. The thermal insulance of a struct ...

Music

* '' ’u’'', the first opera in the Klingon language * "u" (Kendrick Lamar song), 2015 * "U" (Super Junior song), 2006 * ''U'' (album), a 1970 double album by the Incredible String Band * ''U'' (NiziU album), an album by NiziU, released in 2021 * "U", a song by KNK from '' Remain'' * "U", a song by Pearl Jam on their album ''

Lost Dogs Lost Dogs are an American musical supergroup formed in 1991, comprising vocalists, songwriters, and guitarists from multiple Christian alternative rock bands. Their current lineup includes Terry Scott Taylor (Daniel Amos, the Swirling Eddies) ...

'' * "U", a song by S.E.S., released in 2002 * "U", an album by

The Enid The Enid are a British progressive rock band founded by keyboardist and composer Robert John Godfrey. Godfrey received his main musical education from The Royal College of Music. He is previously known for his work with Barclay James Harvest, ...

, released in 2019 * "U", a song by

Treasure (band) Treasure (; Japanese: トレジャー; stylized in all caps) is a South Korean boy band formed in 2019 by YG Entertainment through the reality-survival program ''YG Treasure Box'' (2018–2019). The band consists of 10 members: Choi Hyun-suk, ...

, released in 2022

People

* An honorific used in

Burmese names Burmese names lack the serial structure of most Western names. The Burmans have no customary matronymic or patronymic system and thus there is no surname at all. In the culture of Myanmar, people can change their name at will, often with no go ...

* An alternative spelling of

Woo (Korean name) Woo, also spelled Wu or Wo, Ou, U, is an uncommon List of Korean surnames, Korean surname, a single-syllable Korean given name, and an element in many two-syllable Korean given names. As given name meaning differs based on the hanja used to write ...

, including a list of people with that family or given name *

U of Goryeo U of Goryeo (25 July 1365 – 31 December 1389) ruled Goryeo (Korea) as the 32nd king from 1374 until 1388. He was the only son of King Gongmin. Cultural background In the thirteenth century, Mongol forces had invaded China and established the ...

(1363–1389), king of Goryeo (Korea), often called King Woo

Places

U, Pohnpei U, also written Uh, is one of the administrative divisions of Pohnpei State, Federated States of Micronesia. U bears the shortest place name in the Federated States of Micronesia, and one of the shortest in the world. Description U is one of the ...

, Federated States of Micronesia *

Ü-Tsang Ü-Tsang is one of the three traditional provinces of Tibet, the others being Amdo in the north-east, and Kham in the east. Ngari (including former Guge kingdom) in the north-west was incorporated into Ü-Tsang. Geographically Ü-Tsang covered ...

, one of three historical provinces of Tibet **

Ü (region) Ü () is a geographic division and a historical region in Tibet. Together with Tsang (, ), it forms Central Tibet Ü-Tsang (, ), which is one of the three Tibetan regions or ''cholka'' (). The other two ''cholka'' are Kham (, ) (Dotod) and Amdo ...

, a particular region of Ü-Tsang

Education

University A university () is an institution of higher (or tertiary) education and research which awards academic degrees in several academic disciplines. Universities typically offer both undergraduate and postgraduate programs. In the United States ...

, commonly abbreviated "U"

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) The cuneiform U sign is found in both the 14th century BC Amarna letters and the ''Epic of Gilgamesh''. It can be used for the alphabetic ''u'', instead of the more common 2nd u, (ú). It has two other uses, commonly. It can be used for th ...

, a cuneiform sign *

U (Cyrillic) U (У у; italics: ) is a letter of the Cyrillic script. It commonly represents the close back rounded vowel , somewhat like the pronunciation of in "boot" or rule. The forms of the Cyrillic letter U are similar to the lowercase of the Lat ...

, 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 Romanian letter se * ''u'', an abbreviation for "

you In Modern English, ''you'' is the second-person pronoun. It is grammatically plural, and was historically used only for the dative case, but in most modern dialects is used for all cases and numbers. History ''You'' comes from the Proto- ...

" 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 A content rating (also known as maturity rating) rates the suitability of TV shows, movies, comic books, or video games to this primary targeted audience. A content rating usually places a media source into one of a number of different categories, ...

used in the following countries: **

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

, issued by the British Board of Film Classification **

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

, issued by the Central Board of Film Certification **

Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...

, issued by the Film Censorship Board of Malaysia **

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...

, documented at Censorship in France ** Latvia, Malaysia and Malta, documented at

Motion picture content rating system A motion picture content rating system classifies films based on their suitability for audiences due to their treatment of issues such as sex, violence, or substance abuse; their use of profanity; or other matters typically deemed unsuitable for c ...

and

Television content rating system Television content rating systems are systems for evaluating the content and reporting the suitability of television programs for minors. Many countries have their own television rating system and countries' rating processes vary by local prio ...

U (TV channel) U was an interactive youth-oriented New Zealand television channel, owned and operated by TVNZ. The channel launched on 13 March 2011, and featured reality programming, as well as an interactive live show and music content. It replaced the no ...

, a former television channel in New Zealand * U, the production code for the 1965 ''Doctor Who'' serial ''

The Myth Makers ''The Myth Makers'' is the third serial of the third season of the British science fiction television series ''Doctor Who''. Written by Donald Cotton and directed by Michael Leeston-Smith, the serial was broadcast on BBC1 in four weekly parts ...

'' *The American Spanish-language network

Univision Univision () is an American Spanish-language free-to-air television network owned by TelevisaUnivision. It is the United States' largest provider of Spanish-language content. The network's programming is aimed at the Latino public and includes ...

has the U logo

Other uses

U Mobile U Mobile Sdn Bhd (223969-U) is a Malaysian mobile telecommunications service provider and was founded in 1998 as MiTV Networks Sdn Bhd. U Mobile is a wholly owned subsidiary of U Television Sdn Bhd, which was formerly known as U Telecom Media ...

, Malaysian mobile phone and data service provider * U-bend, a U-shaped plumbing trap *

U bolt A U-bolt is a bolt in the shape of the letter U with screw threads on both ends. U-bolts have primarily been used to support pipework Within industry, piping is a system of pipes used to convey fluids (liquids and gases) from one locati ...

, a U-shaped metal fastener * Ⓤ, (U inside a circle),

hechsher A hechsher (; he, הֶכְשֵׁר "prior approval"; plural: ''hechsherim'') is a rabbinical product certification, qualifying items (usually foods) that conform to the requirements of halakha. Forms A hechsher may be a printed and signed certi ...

or kosher certification by the Orthodox Union * U, =U= or -U-, symbol for

Ustaše The Ustaše (), also known by anglicised versions Ustasha or Ustashe, was a Croatian fascist and ultranationalist organization active, as one organization, between 1929 and 1945, formally known as the Ustaša – Croatian Revolutionary Move ...

Croatian movement * Nickname for football teams: ** La U or

Universitario de Deportes Club Universitario de Deportes, popularly known as Universitario or simply as La "U", is a Peruvian football club located in Lima. The club was founded in 1924 under the name Federación Universitaria by students of the National University of S ...

, Peru **

Universitatea Cluj Fotbal Club Universitatea Cluj (), commonly known as Universitatea Cluj or simply as U Cluj, is a Romanian professional association football, football club based in the city of Cluj-Napoca, Cluj County, that competes in the Liga I, the first ...

, Romania * U, the color blue in ''

Magic: The Gathering ''Magic: The Gathering'' (colloquially known as ''Magic'' or ''MTG'') is a Tabletop game, tabletop and Digital collectible card game, digital Collectible card game, collectable card game created by Richard Garfield. Released in 1993 by Wizards ...

'' *

Wii U The Wii U ( ) is a home video game console developed by Nintendo as the successor to the Wii. Released in late 2012, it is the first eighth-generation video game console and competed with Microsoft's Xbox One and Sony's PlayStation 4. Th ...

, the sixth Nintendo video game home console, released in 2012 *

Uniform A uniform is a variety of clothing worn by members of an organization while participating in that organization's activity. Modern uniforms are most often worn by armed forces and paramilitary organizations such as police, emergency services, ...

, 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 An underscore, ; also called an underline, low line, or low dash; is a line drawn under a segment of text. In proofreading, underscoring is a convention that says "set this text in italic type", traditionally used on manuscript or typescript a ...

, originally invoked in HTML using * U, a brand of feminine pads by

Kotex Kotex is an American brand of menstrual hygiene products, which includes the Kotex maxi, thin and ultra thin pads, the Security tampons, and the Lightdays pantiliners. Most recently, the company has added U by Kotex to its line of menstrual ...

* U, the logo for

Unilever Unilever plc is a British multinational consumer goods company with headquarters in London, England. Unilever products include food, condiments, bottled water, baby food, soft drink, ice cream, instant coffee, cleaning agents, energy dri ...