The terms moot, mootness and moot point are used in both in English and American law, although with different meanings.

In the legal system of the United States, a matter is "moot" if further legal proceedings with regard to it can have no effect, or events have placed it beyond the reach of the law. Thereby the matter has been deprived of practical significance or rendered purely academic. The U.S. development of this word stems from the practice of moot courts, in which hypothetical or fictional cases were argued as a part of legal education. These purely academic issues led the U.S. courts to describe cases where developing circumstances made any judgment ineffective as "moot". The doctrine can be compared to the ripeness doctrine, another judge-made rule, that holds that judges should not rule on cases based entirely on anticipated disputes or hypothetical facts. Similar doctrines prevent the federal courts of the United States from issuing advisory opinions.

This is different from the usage in the British legal system, where the term "moot" has the meaning of "remains open to debate" or unresolved. The shift in usage was first observed in the United States and the extent to which the term is used in U.S. jurisprudence and therefore the meaning attached to it has had the effect that it is rarely if ever used in a British courtroom. It should not be confused with the term "moot court", which refers to practice appellate arguments.