Literally a vicar apostolic is a representative of the Apostolic See. He is a prelate, possesses episcopal ordination, and is entrusted with a specific territory (the vicariate apostolic), which does not, however, have the canonical status of a diocese nor the autonomy of a diocese vis-à-vis Rome. It is a way the church is organized in mission territories. The vicar apostolic is the local ordinary and possesses potestas ordinaria vicaria.
G. Bier, in: Münsterischer Kommentar zum Codex iuris canonici, 1997, c. 371 (loose-leaf ed.).