1. Games A playing card whose value can vary as determined by its holder.

2. Sports An athlete or team selected to compete in a tournament or playoff from among those who did not qualify by meeting the regular requirements.

3. Computers A symbol that stands for one or more unspecified characters, used especially in searching text and in selecting multiple files or directories.

4. Slang An unpredictable or unforeseeable factor: A surprise witness proved to be the wild card at the trial.