A probability under certain conditions, also known as a conditional probability. P(A | B) means the probability of A, given that all we know is the conditions B.
The probability that an event occurs with evidence both about the prior probability and also about the current case in question. See: Bayes' Theorem, Prior Probability.
The posterior probability of a random event or an uncertain proposition is the conditional probability it is assigned when the relevant evidence is taken into account.