U (disambiguation)

U is the twenty-first letter of the Latin alphabet.

U may also refer to:

Science

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