Mu (letter)
| Greek letters | |
| 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 |
| Greek alphabet | |
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.
The lower-case letter μ is used as the symbol for:
- The MÃÂöbius function in mathematics.
- The SI prefix micro-, which represents one millionth, or 10-6.
- Formerly, the micron, an old unit corresponding to the micrometer.
- The coefficient of friction, ie. the ratio of the limiting frictional force between two surfaces against the normal contact force.
- The elementary particle called muon in particle physics.
- Reduced mass in the two-body problem in physics.
- Rarely, to distinguish between one item represented by m and another (but m might be an easier option).
- The permeability in physics and electrical engineering.