Mu

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