vicar apostolic

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A titular bishop who administers a region that is not yet a diocese as a representative of the Holy See.
• noun A titular bishop appointed to administer to a vacant see in which the succession of bishops has been interrupted.
• noun A bishop or an archbishop formerly delegated by the pope to act in his stead in a particular region.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A Roman Catholic with the title of bishop who administers a region that is not (yet) a diocese, especially in a missionary position

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a titular Roman Catholic bishop in a non-Catholic area