wild card

Short definition from Wiktionary

Noun

1. 1
   A card that can be assigned any value or used to substitute for any needed card.
2. 2
   A competitor or team that is allowed to compete in a tournament despite not reaching the normal standards to qualify for inclusion.
3. 3
   Alternative form of wildcard (“substituted text character”).
4. 4
   Alternative form of wildcard (“symbol for a generic sound”).
5. 5
   Alternative form of wild card.