Disjoint

$$\text{Disjoint(A,B)}\equiv A\cap B=\varnothing$$

Disjoint Events

A special case of Principle of Inclusion-Exclusion for Probability, when all events are Disjoint. This is because all terms after the first term are the Empty Set $\varnothing$

$$P\left(\bigcup _{i=1}^{\infty }{A}_i\right)=\sum _{i=1}^{\infty }P(A_i)$$