What term describes an order signed by a magistrate directing a sheriff to imprison a person?

The correct term that describes an order signed by a magistrate directing a sheriff to imprison a person is "commitment." A commitment order is a legal document that authorizes the detention of an individual, typically after a finding of probable cause. This document is issued after the magistrate reviews the circumstances of a case and decides that the individual should be held in custody, either awaiting trial or as part of a sentence.

In contrast, a warrant is a broader term related to law enforcement that authorizes actions such as arrests or searches but does not specifically mandate imprisonment. A subpoena is a legal document requiring a person to appear in court or produce evidence but does not involve imprisonment. An indictment, on the other hand, is a formal accusation indicating that a person has been charged with a crime, but it is not an order for imprisonment on its own. The commitment is specific to the act of directing a sheriff to detain a person, making it the most accurate term in this context.