Glossary

Intersection

The intersection of two sets is the new set formed by taking those elements that are contained in both sets. If $A$ and $B$ are sets, then their intersection is written $A \cap B$. As a result of this definition, $A \cap B$ is a subset of both $A$ and $B$. Compare to the union $A \cup B$, which is the collection of elements contained in either set.

In the standard figure below, two sets are represented by circles (shaded white), and their intersection has been shaded red.

Intersection

Wikipedia