detainer

noun | \ di-ˈtā-nər \ | de·tain·er

1. : the act of keeping something in one's possession; specifically : unlawful detainer : unlawful detainer

2. : detention in custody

3. : a notification sent by a prosecutor, judge, or other official advising a prison official that a prisoner is wanted to answer criminal charges and requesting continued detention of the prisoner or notification of the prisoner's impending release — compare extradition