Is there a name for a function which produces the same result when reapplied?

Question

Is there a name for a function which, when applied to its own result, will always return that same result?

e.g. for a function $f(x) = ||x||$

$f(2.5) = 2$

and

$f(f(2.5)) = 2$

Answer 1

I would say that the common name is idempotent, see https://en.wikipedia.org/wiki/Idempotence