TITLE: Is there a name for functions that are their own inverses
QUESTION [6 upvotes]: There are terms for various kinds of functions (or operators) such as...
associative - (a # b) # c  =  a # (b # c)
commutative - a # b  =  b # a
idempotent  - f (f (x)) = f (x)

Is there a similar name for functions that are their own inverse?
f (f (x)) = x

REPLY [13 votes]: It is called as an involution.

REPLY [6 votes]: Such a function is called an involution.