Writ

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

Additional Sources

Answers.com

A written order issued by a court, commanding the party to whom it is addressed to perform or cease performing a specified act.

Duhaime Legal Dictionary

An official court document, signed by a judge or bearing an official court seal, which commands the person to whom it is addressed, to do something specific.

Encyclopedia Britannica

In common law, order issued by a court in the name of a sovereign authority requiring the performance of a specific act. The most common modern writs are those, such as the summons, used to initiate an action. Other writs may be used to enforce the judgment of a court (attachment, delivery) or to require a lower court to furnish certain records (error) or perform a certain act (mandamus).

Wikipedia

In law, a writ is a formal written order issued by a body with administrative or judicial jurisdiction; in modern usage, this public body is generally a court. Warrants, prerogative writs and subpoenas are types of writs; there are many others.