Intersection[, , ... ] gives a sorted list of the elements common to all the .
If the are considered as sets, Intersection gives their intersection.
Intersection[, , ... ] can be input in StandardForm and InputForm as ... . The character can be entered as inter or \[Intersection].
The must have the same head, but it need not be List.
Intersection[, ... , SameTest->test] applies test to each pair of elements in the to determine whether they should be considered the same.
Intersection[a, b] can be entered in StandardForm and InputForm as a b or a \[Intersection] b.
See The Mathematica Book: Section 1.8.8.
See also: Union, Complement.