A lowercase Greek letter commonly representing means in statistics, coefficients in physics, and measures in analysis.
Examples
Mean of a probability distribution
\mu = \frac{1}{n}\sum_{i=1}^{n} x_i
Coefficient of friction in physics
F_f = \mu N \text{ (friction force equation)}
Micro prefix in units
\text{Capacitance} = 47\mu\text{F}