wildcard

Etymology

wild + card

noun

1. (computing) A character that takes the place of any other character or string that is not known or specified.
   1968, Digital Equipment Corporation, VAX/VMS 319(5864), page 751, Section 2.1.2 Using Wildcard Characters A wildcard character is a symbol that you can use with many DCL commands to apply the command to several files at once, rather than specifying each file individually.
   If the character * is acting as a wildcard, then the pattern a*m matches each of the words amalgam, atom and alum.
2. (also written wild card) An uncontrolled or unpredictable element.
   There are several technical wildcards, such as how the larger battery packs--four times larger than those of the Prius--will withstand the rigors of city driving, […] February 8 2008, Eli Kintisch, “From Gasoline Alleys to Electric Avenues”, in Science, 319(5864), page 751
3. (also written wild card) An element, often deliberately concealed, which is withheld for contingency.
4. (sports, card games) Alternative form of wild card.
   German wildcard Sabine Lisicki conquered her nerves to defeat France's Marion Bartoli and take her amazing Wimbledon run into the semi-finals. June 28, 2011, Piers Newbery, “Wimbledon 2011: Sabine Lisicki beats Marion Bartoli”, in BBC Sport