what does mutually exclusive mean

Mutually exclusive means two or more events, outcomes, or statements cannot occur or be true at the same time. In probability terms, events A and B are mutually exclusive if P(A and B) = 0, which means their intersection is empty. For example, in a single coin toss, 'heads' and 'tails' are mutually exclusive because you cannot get both on the same toss. In everyday use, mutually exclusive options force a single choice rather than allowing both. For a set of events, the set is mutually exclusive if no pair of events in the set can happen together. Note that mutually exclusive is different from independent: mutually exclusive events (with nonzero probability) are not independent, because if one occurs it rules out the other.