wild card

from WordNet (r) 3.0 (2006)

wild card
    n 1: an unpredictable factor; "the weather was a wild card"
    2: a playing card whose value can be determined by the person
       who holds it

from The Free On-line Dictionary of Computing (8 July 2008)

wild card

   <operating system, programming, text> (From card games in
   which certain cards, often the joker, can act as any other
   card) A special character or character sequence which matches
   any character in a string comparison, like ellipsis ("...") in
   ordinary written text.

   In {Unix} filenames '?' matches any single character and '*'
   matches any zero or more characters.  In {regular
   expressions}, '.' matches any one character and "[...]"
   matches any one of the enclosed characters.

   See also {Backus-Naur Form}.

   (1997-07-16)