In the field of computation theory, star is one of the regular operations. If `A` is a language (not necessarily a regular language) then `A`* (read "`A` star") is defined as follows.

{`x`_{1}`x`_{2}…`x`_{k}
| `k` ≥ 0 and each `x`_{i} ∈ `A`}

In plain English: `A`* is the set of all strings made up of any number of consecutive strings in `A`, including 0.

For example, if `A` = {0,1},

`A`* = {ε, 0, 1, 00, 01, 10, 11, 000, 001, 010, 011, …}

Some interesting things to note about the star operation:

`A`* always contains the empty string (ε ∈ `A`)
`A`* is a superset, though not necessarily a proper superset, of `A`* (`A`* ⊇ `A`)
- Regular languages are closed under the star operation. This means that if
`A` is a regular language, then so is `A`*.