1. (computing) describing an action which, when performed multiple times, has no further effect on its subject after the first time it is performed.
2. said of an element of an algebraic structure (such as a group or semigroup) with a binary operation: that when the element operates on itself, the result is equal to itself.
3. said of a binary operation: that all of the distinct elements it can operate on are idempotent (in the sense given just above).
4. an idempotent ring or other structure

1. in multiple algebra, a quantity which multiplied into itself gives itself. ordinary unity is idempotent.

1. unchanged in value following multiplication by itself