Bayes' theorem

n. In statistics, a formal expression of the probability that one event will occur, given that another event occurs when the usual probabilities of the events are known. In written form, the probability of any event A given the occurrence of another event B, P(A/B), is given by the formula P(B) where P(A) is the prior probability of event A, P(B) is the prior probability of event B, and P(B/A) is the prior probability of event B given the occurrence of event A.