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)