U (disambiguation)

Last updated January 14, 2026

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

Science

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

<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 44.50 millimetres (1.75 in)
U, universal Turing machine
The prefix U+ (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 ⟨U⟩ and ⟨u⟩ are given formally as U+0055ULATIN CAPITAL LETTER U and U+0075uLATIN SMALL LETTER U.

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

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.

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

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

/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

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

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

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