Mutually exclusive events

Mutually exclusive events cannot both occur on the same trial, so they share no outcomes.

Two events are mutually exclusive, or disjoint, when they have no outcomes in common, so if one happens the other cannot. For example, on a single die roll, rolling a 2 and rolling a 5 are mutually exclusive. For such events the addition rule simplifies to $P(A \text{ or } B) = P(A) + P(B)$ . Being mutually exclusive is about overlap, which is different from being independent.