A lowercase Greek letter commonly used to denote angles, scaling factors, or significance levels in mathematics and statistics.
Examples
Angle measurement
\sin \alpha = \frac{\text{opposite}}{\text{hypotenuse}}
Statistical significance level
H_0 \text{ is rejected at } \alpha = 0.05 \text{ level}
Physics decay constant
N(t) = N_0e^{-\alpha t}