Constitutional Law
Mootness
Definition
A case is moot when the controversy between the parties has been resolved, or the plaintiff no longer has a legally cognizable interest in the outcome. Under Article III, federal courts can only decide actual, live controversies. Exceptions to mootness include cases that are capable of repetition yet evading review, voluntary cessation by the defendant (which does not moot a case if the behavior could recur), and class actions where the named plaintiff's claim expires but the class retains a live controversy.
Example
A student sues a university for an unconstitutional policy but graduates before the case is decided. The case may be moot unless it falls within the capable-of-repetition exception.