Mu can be:

• Mu, Μ or μ, a letter in the Greek alphabet.

μ is used as a symbol for:

• • The SI prefix micro, meaning a factor of 10^-6 (one millionth).
    • μ by itself is often used as the "unit" of strain, though in this context it retains its SI prefix meaning, which is interchangeable with "x 10^-6" or "ppm" (parts per million).
    • μ by itself is an abbreviation for the unit micron. Both the term and the abbreviation should not be used. The preferred terms are µm and micrometre
  • In mathematics,
    • The arithmetic mean of a statistical population
    • The Möbius function
    • The least-fixed-point-operator
    • A degree of membership from a fuzzy set.
  • In chemistry,
    • The chemical potential
  • In physics,
    • The coefficient of friction
    • The mobility coefficient
    • The permeability (electromagnetism) coefficient
    • The muon, an elementary particle
    • The standard gravitational parameter
    • The magnetic dipole moment
    • The linear density
    • Viscosity
    • Reduced mass
  • µTorrent, a freeware BitTorrent client for Microsoft Windows written in C++.
  • μZiq, An alias of Mike Paradinas.

In Asian languages:

• Mù, (穆), a Chinese surname
• Mu (unit of area) (亩/畝), a Chinese unit of area
• Mu (kana), represented by the Japanese kana む or ム
• Mu (negative) (無), a Japanese word important in Zen koan practice

Mu may also refer to:

• Muonium's atomic symbol
• Mu-metal, an alloy used for screening magnetic fields
• Mu (lost continent), a mythical continent in the Pacific Ocean subsequently appearing in several books, films, and games
• Mu (rocket), a Japanese rocket
• Mu Dan, Chinese poet and translator
• Mu Online, an online role-playing game
• Mu La Flaga, a character from the anime Mobile Suit Gundam SEED
• Aries Mu, a character from the cartoon Saint Seiya
• Groupe Mu, an interdisciplinary Belgian group focusing on linguistics and rhetoric
• Lemuria, a hypothetical lost continent

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
• MU puzzle, a puzzle in Gödel, Escher, Bach
• University of Mumbai, formerly called the University of Bombay
• Marquette University
• Marshall University
• Miami University, a public university in Oxford, Ohio
• Millersville University of Pennsylvania
• Miskatonic University
• University of Missouri, a public university in Columbia, Missouri
• Mahidol University, a University in Thailand
• Manipal University, a university in Karnataka, India
• MU (70's band), an early 1970s psychedelic group led by Merrell Fankhauser and Jeff Cotton
• MU (00's band), a 00's electro-punk group made up of producer Maurice Fulton and his wife Mutsumi Kanamori.
• Mirror Universe (Star Trek), fictional parallel universe in which the plots of several Star Trek television episodes take place
• Magic-User, a class type in D&D, HackMaster, and many fantasy RPGs
• Musician, an enlisted rating in the United States Navy
• Isuzu MU Wizard
• Micron Technology