Kleene star
Also known as: Kleene closure
Kleene star (or Kleene closure) is a unary operation in computer science and formal language theory that means “zero or more” repetitions of a set of symbols or strings.
If $L$ is a language, $L^*$ contains the empty string and every string made by concatenating zero or more strings from $L$. In a regular expression, a* matches the empty string, a, aa, and so on.