wildcard

Short definition from Wiktionary

Noun

1. 1
   A character that takes the place of any other character or string that is not known or specified.
2. 2
   An uncontrolled or unpredictable element.
3. 3
   An element, often deliberately concealed, which is withheld for contingency.
4. 4
   Alternative form of wild card.
5. 5
   A letter or symbol that substitutes for a generic or poorly identified sound, for example capital C for any or some consonant, or capital V for any or some vowel.

Verb

1. 1
   To replace or supplement with a wildcard character to allow matching against a range of possible values.