wildcard

Wildcard is a term used in computing and information technology to denote a character or string that can represent one or more unspecified characters. It enables pattern matching and flexible searches across files, databases, or text, without listing every possible value.

Wildcards are implemented as special characters, with the asterisk (*) and the question mark (?) being the most common. An asterisk matches any sequence of characters, while a question mark matches a single character. Some contexts support character classes or switch to regular expressions. Glob patterns, used by shells and file managers, are a simple form of wildcard matching, whereas regular expressions offer more complex rules. In SQL, the LIKE operator uses % for any sequence and _ for a single character, which is similar to wildcards but with different syntax.

DNS wildcards allow a single record to match multiple subdomains, such as *.example.com. Wildcard certificates authorize encryption for all subdomains of a domain under one certificate. They simplify management but can broaden risk if a private key is compromised.

Beyond computing, wildcards appear in games and sports. A wildcard card, such as a joker, can substitute for other cards. In sports, a wildcard entry refers to a team’s admission to a competition outside automatic qualification, often based on performance. The term also describes any uncertain or variable element in a process or dataset.