<operating system, programming, text> (From card games in which certain cards, often the joker, can act as any other card) A special character or character sequence which matches any character in a string comparison, like ellipsis ("...") in ordinary written text.
In Unix filenames '?' matches any single character and '*' matches any zero or more characters. In regular expressions, '.' matches any one character and "[...]" matches any one of the enclosed characters.
See also Backus-Naur Form.