Statistics, Mathematics. the probability that an event will occur under the condition that another event occurs first: equal to the probability that both will occur divided by the probability that the first will occur.
British Dictionary definitions for conditional probability
conditional probability
noun
1.
(statistics) the probability of one event, A, occurring given that another, B, is already known to have occurred: written P(A|B) and equal to P(A and B)|P(B)