Habeas corpus is a recourse in law by which a report can be made to a court in the events of unlawful detention or imprisonment, requesting that the court order the person's custodian to bring the prisoner to court, to determine whether their detention is lawful.

In common law, a writ is a formal written order issued by a body with administrative or judicial jurisdiction; in modern usage, this body is generally a court. Warrants, prerogative writs, subpoenas, and certiorari are common types of writs, but many forms exist and have existed.