in partibus infidelium

Etymology
, so named because such bishops were assigned sees corresponding to territories that had passed under the control of other religions, and so did not imply a duty of residence or diocesan responsibilities.

Adjective

 * 1)  Of a bishop or see: merely titular, without regular jurisdiction, and serving to assist some other bishop or to act as delegates of the pope where no hierarchy had yet been established.

Usage notes
The term in partibus infidelium was formally suppressed by the Catholic Church in 1882, and such bishops are now officially known as titular bishops.