Mu (letter)

Greek alphabet
Α α Alpha;	Β β Beta;
Γ γ Gamma;	Δ δ Delta;
Ε ε Epsilon;	Ϝ ϝ Digamma;
Ζ ζ Zeta;	Η η Eta;
Θ θ Theta;	Ι ι Iota;
Κ κ Kappa;	Λ λ Lambda;
Μ μ Mu;	Ν ν Nu;
Ξ ξ Xi;	Ο ο Omicron;
Π π Pi;	Ϻ ϻ San;
Ϙ ϙ Qoppa;	Ρ ρ Rho;
Σ σ Sigma;	Τ τ Tau;
Υ υ Upsilon;	Φ φ Phi;
Χ χ Chi;	Ψ ψ Psi;
Ω ω Omega;	Ϡ ϡ Sampi;

Mu (upper case Μ, lower case μ) is the 12th letter of the Greek alphabet. In the system of Greek numerals it has a value of 40. In the ISO 8859 character encodings standard, it has an ordinal decimal value of 230.

The lower-case letter μ is used as a special symbol in many academic fields.

• In mathematics:
  • the Möbius function in number theory
  • the population mean or expected value in probability and statistics
  • a measure in measure theory
• In measurement:
  • the SI prefix micro-, which represents one millionth, or 10⁻⁶
  • the micron, an old unit which corresponds to the micrometre (which is now denoted "µm")
• In classical physics and engineering:
  • the coefficient of friction
  • reduced mass in the two-body problem
  • permeability in electromagnetism
• In particle physics:
  • the elementary particle called the muon

Rarely, the letter μ may be used to distinguish one item represented by "m" from another (but a better option might be to use "m", "m", "m", etc.).

Letters that arose from the Greek Μ include the Latin M and Cyrillic М.

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