Periodic Point

A point $x_0$ is said to be a periodic point of a Function $f$ of period $n$ if $f^n(x_0)=x_0$, where $f_0(x)=x$ and $f^n(x)$ is defined recursively by $f^n(x)=f(f^{n-1}(x))$.

See also Least Period, Periodic Function, Periodic Sequence