What does the letter f mean in probability?

Answer 1

The answer depends on the context and also whether it is upper or lower case.

f can refer to

• the frequency of an outcome in repeated trials,
  
• the probability distribution function for a continuous variable.

F can refer to

• the cumulative distribution function for a continuous variable,
  
• Fisher's F-distribution which, in the form of Fisher's F-statistic is used for comparing variances.

There are probably other meanings.