f :

An F score is a score on the F distribution.

The F distribution is a distribution of ratios of variances from a normal distribution. It can be used to determine if two variances are probably from the same distribution of variances.

F scores are best known from their role in analysis of variance, or ANOVA. In an ANOVA, the size of the F score roughly corresponds to the size of the effect. An F of 1 or less than 1 means that no effect is present at all. A large F corresponds to a strong effect.