An apostolic vicariate is a territorial jurisdiction of the Catholic Church under a titular bishop centered in missionary regions and countries where dioceses or parishes have not yet been established.
The hope is that the region will generate sufficient numbers of Catholics for the Church to create a diocese one day.
It is exempt under canon law, directly subject to the missionary Dicastery for Evangelization of the Vatican in Rome.
The less developed instance is the mission sui iuris, which other than the ones mentioned before is not a particular church, although it shares some similarities to one; at its head, an ecclesiastical superior is named.
The apostolic vicariate is distinguished from a territorial abbacy (or "abbey nullius")—an area not a diocese but under the direction of the abbot of a monastery.