A diocese is the geographic area under the pastoral care of a particular bishop.
Originally a territorial unit of imperial Roman governance, as church administrative divisions came to align roughly with such secular borders, the Church eventually adopted the term as well. Today, dioceses often follow secular territorial borders, but are not canonically required to do so.
It should be noted that in Greek, diocese (διοικησις) often refers to the area included in the territory of an autocephalous or autonomous church, while parish (παροικια) is the term for the territory of a bishop.
Types of dioceses
There are several types of dioceses in the Orthodox Church:
- Eparchy: a general term for an ecclesiastical province, though often used technically to refer to the territory over which the primate, often referred to as an eparch, has immediate jurisdictional authority (e.g., Moscow and its immediate environs are the eparchy of the Patriarch of Moscow and All Russia).
- Exarchate: often a missionary diocese, though traditionally referring to a diocese in which there is only one bishop (or other cleric) with authority, who is often referred to as an exarch.
- Metropolis (or metropolia or metropolitanate): an ancient diocese (especially in Byzantine areas) or set of dioceses with a metropolitan as the ruling bishop or primate. A metropolis may have constituent dioceses.
- Archdiocese: a large or important diocese or set of dioceses whose primate or ruling bishop is an archbishop. An archdiocese may have constituent dioceses.
These terms have shifted a bit over time and in different regions, and so usage is not consistent in historical or contemporary sources, whether primary or secondary. Most of these terms also have their origins in Roman civil administrative usage.