- any of the churches originating in countries formerly part of the Eastern Roman Empire, observing an Eastern rite and adhering to the Niceno-Constantinopolitan Creed; Byzantine Church.
- Orthodox Church (def. 2).
- any of the Christian Churches of the former Byzantine Empire
- any Church owing allegiance to the Orthodox Church and in communion with the Greek patriarchal see of Constantinople
- any Church, including Uniat Churches, having Eastern forms of liturgy and institutions
