A character that may be substituted for any of a defined subset of all possible characters. Note 1: 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. " Note 2: Whether the wildcard character represents a single character or a string of characters must be specified. 2. In computer (software) technology, a character that can be used to substitute for any other character or characters in a string. Note: The asterisk (*) usually substitutes as a wildcard character for any one or more of the ASCII characters, and the question mark (?) usually substitutes as a wildcard character for any one ASCII character.