U (disambiguation)
U, or u, is the twenty-first letter of the English alphabet. U may also refer to: == Science == === Mathematics === ∪ {\displaystyle \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 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).