Disjoint Sets

Two sets and are disjoint if they have no elements in common, i.e., their intersection is empty:

A collection of sets is called pairwise disjoint (or mutually disjoint) if every pair of distinct sets in the collection is disjoint:

Example

The sets and are disjoint.
The sets of even and odd integers are disjoint.
The intervals and on the real line are disjoint.