Ecclesiology

"Pentarchy" (from the Greek Πενταρχία, Pentarchia from πέντε pente, "five", and ἄρχειν archein, "to rule") is a model historically championed in Eastern Christianity as a model of church relations and administration.

Caesaropapism /ˌsiːzəroʊˈpeɪpɪzəm/ is the idea of combining the power of secular government with the religious power, or making it superior to the spiritual authority of the Church; especially concerning the connection of the Church with government.

The Christian Church is a term used by some to refer to the whole group of people belonging to the Christian religious tradition throughout history.

The word diocese is derived from the Greek term διοίκησις meaning "administration".

Ecumenism refers to efforts by Christians of different church traditions to develop closer relationships and better understandings.

In the Christian churches, holy orders are ordained ministries such as bishop, priest or deacon.

Lumen gentium, the Dogmatic Constitution on the Church, is one of the principal documents of the Second Vatican Council.

Presbyterian (or presbyteral) polity is a method of church governance ("ecclesiastical polity") typified by the rule of assemblies of presbyters, or elders.

Apostasy in Christianity is the rejection of Christianity by someone who formerly was a Christian.

Sister Churches is a term used in 20th-century ecclesiology to describe ecumenical relations between the Roman Catholic Church and the Eastern Orthodox Churches, and more rarely and unofficially, between the Roman Catholic Church and the Anglican communion.

The Four Marks of the Church is a term describing four specific adjectives — one, holy, catholic and apostolic — indicating four major distinctive marks or distinguishing characteristics of the Christian Church.

Christendom has several meanings.