The term wildcard character has the following meanings:

Telecommunication

In telecommunications, a wildcard character is a character that may be substituted for any of a defined subset of all possible characters.

• In high-frequency (HF) radio automatic link establishment, the wildcard character "?" may be substituted for any one of the 36 characters, "A" through "Z" and "0" through "9."
• Whether the wildcard character represents a single character or a string of characters must be specified.

Computing

In computer (software) technology, a wildcard character can be used to substitute for any other character or characters in a string.

The asterisk (*) usually substitutes as a wildcard character for any zero or more characters, and the question mark (?) usually substitutes as a wildcard character for any one character, as in the CP/M, DOS, Microsoft Windows and POSIX (Unix) shells. (In Unix this is referred to as glob expansion.) In SQL, the wildcard characters are percent (%) for zero or more characters, and underscore (_) for one character. In many regular expression implementations, the period (.) is the wildcard character for a single character.

Source: originally from Federal Standard 1037C and from MIL-STD-188

See also wild card, glob