Eparchy is an anglicized Greek word (Koinē Greek: ἐπαρχία, romanized: eparchía, lit.'overlordship', Byzantine Greek pronunciation: [e.parˈçi.a]; abstract noun formed from intensive prefix ἐπι-, epi-, lit.'over-' + ἄρχειν, árchein, lit.'to be ruler'), authentically Latinized as eparchia, which can be loosely translated as the rule or jurisdiction over something, such as a province, prefecture, or territory. It has specific meanings both in politics, history and in the hierarchy of the Eastern Christian churches.

In secular use, the word eparchy denotes an administrative district in the Hellenistic-Roman / Byzantine Empire, or in modern Greece or Cyprus.

In ecclesiastical use, an eparchy is a territorial diocese governed by a bishop of one of the Eastern churches, who holds the title of eparch. It is part of a metropolis. Each eparchy is divided into parishes in the same manner as a diocese of western Christendom. In the Catholic Church, an archieparchy equivalent to an archdiocese of the Roman Rite and its bishop is an archieparch, equivalent to an archbishop of the Roman Rite.