In card games, a card that can represent any other card the holder desires.
Using a wild card in poker makes it easier to form a hand.
In sports, a player or team allowed to participate in a tournament without meeting the usual qualification criteria.
He entered the US Open as a wild card.
wildcard (character)
In computing, a character such as '*' or '?' that can stand for any other character or string in searches or pattern matching.
I used the wildcard '*' in the filename to search for all text files.