数学上，两个集合A和B的交集是含有所有既属于A又属于B的元素，而没有其他元素的集合。

A和B的交集写作"A ∩B"。形式上：

例如：集合{1, 2, 3}和{2, 3, 4}的交集为{2, 3}。数字9 不属于素数集合{2, 3, 5, 7, 11,…}和奇数集合{1, 3, 5, 7, 9, 11,…}的交集。

若两个集合A和B的交集为空，就是说他们没有公共元素，则他们不相交，写作：A ∩B = Ø。例如集合{1, 2}和{3, 4}不相交，写作{1, 2} ∩{3, 4} = Ø。

In mathematics, the intersection A ∩ B of two sets A and B is the set that contains all elements of A that also belong to B (or equivalently, all elements of B that also belong to A), but no other elements.

For explanation of the symbols used in this article, refer to the table of mathematical symbols.