Relative frequency
“a” be number of times event A has occurred among the n reptitions, a / n is relative frequency.
\(f_{A} = \frac{n_{A}}{n}\)
\(f_{A}\) = 1 iff A occurs every time among n repetitions.
\(f_{A}\) = 0 iff A does not occur at all.
As experiment is repeated more times, \(f_{A}\) stabilizes.