Ecclesiology comes from the Greek ἐκκλησία (ekklesia), which entered Latin as ecclesia. The term originally meant simply a gathering or assembly. It is a compound of the Greek preposition ἐκ(ek), which denotes origin, and καλῶ (kalo)—from καλέω (kaleo)—meaning to call, so that the compound word means a calling out, as to a meeting. 

Ecclesiology is an in-depth scriptural and historical examination of the mystery of the Church. Explores the historical origins of contemporary issues in ecclesiology such as universal salvation, Chrisitan unity, authority and collegiality, the role of laity and infallibility.  Additional topics include the mission, membership and ministries of the Catholic Church in the world, and its relationship to other churches.

The Catholic Church is highly organized, with local parishes as its building blocks and a central government in the Vatican. Catholics are defined as those who are in communion with the pope.