In computer science, an alphabet is a finite set of characters or digits. The most common alphabet is {0,1}, the binary alphabet. A finite string is a finite sequence of characters from an alphabet; for instance a binary string is a string drawn from the alphabet {0,1}. An infinite sequence of characters may be constructed from elements of an alphabet as well.

Given an alphabet $\backslash Sigma$, we write $\backslash Sigma^*$ to denote the set of all finite strings over the alphabet $\backslash Sigma$. Here, the $\{\}^*$ denotes the Kleene star operator. We write $\backslash Sigma^\backslash infty$ (or occasionally, $\backslash Sigma^\backslash N$ or $\backslash Sigma^\backslash omega$) to denote the set of all infinite sequences over the alphabet $\backslash Sigma$.

See Also

• Formal language
• Syntax
• Semantics