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) attachment an order to attach specified property; (2) certiorari an order by an appellate court granting or denying a review of judgment ; (3) execution an order to enforce a court judgment; (4) habeas corpus an 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) prohibition the 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.