|a children's mummer's parade, as on the Fourth of July, with prizes for the best costumes.|
|an arrangement of five objects, as trees, in a square or rectangle, one at each corner and one in the middle.|
|2.||sport a player or team that has not qualified for a competition but is allowed to take part, at the organizers' discretion, after all the regular places have been taken|
|3.||an unpredictable element in a situation|
|4.||computing a symbol that can represent any character or group of characters, as in a filename|
An unpredictable person or event, as in Don't count on his supporthe's a wild card, or A traffic jam? That's a wild card we didn't expect. This expression comes from card games, especially poker, where it refers to a card that can stand for any rank chosen by the player who holds it. The term was adopted in sports for an additional player or team chosen to take part in a contest after the regular places have been taken. It is also used in computer terminology for a symbol that stands for one or more characters in searches for files that share a common specification. Its figurative use dates from the mid-1900s.