• The Eastern Orthodox Church: the Eastern Christian churches of Byzantine tradition that adhere to the seven Ecumenical Councils, and are in full communion with the Ecumenical Patriarchate of Constantinople and with each other.
• The Oriental Orthodox Churches: the Eastern Christian churches adhering to the teachings of only the first three Ecumenical Councils (plus the Second Council of Ephesus). This usage is uncommon, except among themselves.
• Eastern Christianity: Any Christian tradition tracing its origins to the East (the Balkans, Asia Minor, the Middle East, Eastern Europe, etc.) including the Eastern Catholic churches. This usage is generally considered improper although it is not uncommon.
• Any Christian faith that adheres to the teachings of the first seven (or three) Ecumenical Councils of the Church.
• Any particular Christian doctrine that is theologically correct.
• Any particular Christian "faith" believed by its followers to be correct by comparison to other faiths. In this sense every Church considers its own faith orthodox.

Note: The Eastern Orthodox and Oriental Orthodox Churches are not in communion and do not represent a unified religious tradition. As such, the term Orthodox Christianity when used to refer to these two Churches collectively refers more to a common Byzantine influence than to doctrinal matters.

See also

• Eastern Catholic Churches
• List of Eastern Orthodox Churches
• List of Oriental Orthodox Churches
• Old Believers, a movement containing a large number of independent Eastern Orthodox denominations, which broke from the Russian Orthodox Church in the 17th century:
• Russian Orthodox Old-Rite Church
• Western Orthodoxy, which is a term usually used to describe parishes that are (Eastern) Orthodox in doctrine and use rites dating from, or developed from rites dating from, the pre-11th century church as it existed in the west, and of which the Orthodox consider themselves to be the continuation. The term is also used by some church bodies associated with the Old Catholic Church, Continuing Anglican Movement, and Liberal Catholic Church.