Probability of any one of two or more events. If A and B are two events, the alternative probability of either one of them is expressed as “p(A or B).”Probability, Conditional Probability : Probability of one event given that another event has already occurred. If A and B are two events, then the probability of A, given that B has occurred, is expressed as “p(A or B).”Probability, Joint Probability : Probability that two (or more) events will both (or all) occur. If A and B are two events, the joint probability of both is expressed as “p(A or B).”Probability Distribution : A listing of all the possible outcomes that might occur and the probability of each possible outcome. The sum of these probabilities must equal 1.