A written court order directing a person to take, or refrain from taking, a certain act.

Source: U.S. Courts

A written court order saying that certain action must be taken. Can be a writ of: (1) attachmentan order to attach specified property; (2) certiorarian order by an appellate court granting or denying a review of judgment ; (3) executionan order to enforce a court judgment; (4) habeas corpusan order to release someone that has been unlawfully imprisoned; (5) mandamus (or mandate)an order to perform any act designated by law to be part of a person's duty or status; or (6) prohibitionthe opposite of a writ of mandate that orders that further proceedings or other official acts be stopped (usually issued from a higher to a lower court).

Source: California Courts.