Infix operator with built-in evaluation rules.
x y is by default interpreted as Intersection[x, y].
The character is sometimes called "cap"; but see also \[Cap].
int gives \[Integral] not \[Intersection].
See The Mathematica Book: Section 1.10.4 and Section 3.10.4.
See also: \[Union] , \[SquareIntersection] , \[Cap] , \[Wedge] .