Definition – Disjoint sets. – Math-reference.net

Definition

Let $A$ and $B$ be sets. We say that the sets $A$ and $B$ are disjoint if

$A\cap{B}=\emptyset$

Pairwise disjoint

Let $\mathcal{F}$ be a family of sets and let $A$ and $B$ be sets in $\mathcal{F}$ . If, for every set $A\in\mathcal{F}$ and $B\in\mathcal{F}$ , we have that $A\cap{B}=\emptyset$ , then we say that the sets in $\mathcal{F}$ are pairwise disjoint.