Mu may be:

• Mu (letter), a letter in the Greek alphabet pronounced "mew" (//). μ is used as a symbol for:
  • The SI prefix micro
  • In mathematics,
    • The arithmetic mean of a statistical population
    • The Möbius function
  • In physics,
    • The friction coefficient
    • The mobility coefficient
    • The permeability (electromagnetism) coefficient
    • The muon
    • The standard gravitational parameter
    • The magnetic dipole moment
    • Reduced mass

Mu may also refer to:

• Mu (Cthulhu mythos), a sunken continent in the Cthulhu mythos
• Mu (negative) (無), a Japanese word important in Zen koan practice
• Mu (lost continent), a mythical continent in the Pacific Ocean
• Mu (rocket), a Japanese rocket
• Mu Dan, Chinese poet and translator
• Mu-metal, an alloy used for screening magnetic fields
• Mu Online, an online role-playing game
• Muonium's atomic symbol
• Mu (unit of area) (亩/畝), a Chinese unit of area
• Mu La Flaga, a character from the anime Mobile Suit Gundam SEED
• MU puzzle, a puzzle in Gödel, Escher, Bach.

MU may stand for:

• Mauritius' ISO 3166-1 alpha-2 country code
• China Eastern Airlines's IATA code
• Manchester United Football club
• The Mothers' Union, global Anglican women's organisation
• Monitor unit, a unit used in radiation therapy
• Centimorgan or "map unit", a unit of recombinant frequency in genetics
• Multiple unit, such as a rail diesel car
• University of Mumbai, formerly called the University of Bombay
• Marquette University
• University of Missouri–Columbia
• Mahidol University, University in Thailand
• MisUnderstood word, a term in Scientology
• Mirror Universe (Star Trek), fictional parallel universe in which the plots of several Star Trek television episodes take place

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