Overview
A territorial prelate is, in Catholic usage, a prelate whose geographic jurisdiction, called territorial prelature, generally does not belong to any diocese and is considered a particular church.
The term is also used in a generic sense, and may then equally refer to an apostolic prefecture, an apostolic vicariate, a permanent apostolic administration (which are pre-diocesan, often missionary, or temporary), or a territorial abbacy (see there).
Status
A territorial prelate exercises quasi-episcopal jurisdiction in a territory separate from the territory of a diocese. In many cases the prelature is exempt from diocesan oversight and instead subject to the jurisdiction of the Holy See.
As a rule, territorial (and personal) prelates are consecrated as bishops, though not bishops of their diocese, as expressed by the title Bishop-prelate. Most were/are missionaries, outside Europe (mainly Latin America and a few Asian countries) or in countries with a Protestant majority (notably Lutheran Norway).
From Wikipedia (CC BY-SA 4.0).