Infix operator with built-in evaluation rules.
x y is by default interpreted as x -> y or Rule[x, y].
x y z groups as x (y z).
\[Rule] is not the same as \[RightArrow].
See The Mathematica Book: Section 1.10.4, Section 3.10.1 and Section 3.10.4.
See also: \[RuleDelayed] .