English version

wild card in Cards topic

From Longman Dictionary of Contemporary Englishwild cardˈwild ˌcard noun [countable]  1 DGCa playing card that can represent any other card2 PREDICTsomeone whose behaviour or effect on a situation is difficult to guess3 a player who is a wild card or who is given a wild card is chosen for a competition although they have not previously done well enough to take part4 technicalTD a symbol that can represent any letter in some computer instructions
Examples from the Corpus
wild cardAt this supreme moment in his plans, in his life, fate had suddenly dealt Jack a wild card.China remains a wild card in the negotiations.But it was like everybody already had their connections, and I was like this wild card.Inevitably I fell for him, thereby complicating my life horrendously and introducing an unexpected wild card into his.