Catechism of the Catholic Church

The word "Church" (Latin ecclesia, from the Greek ek-kalein, to "call out of") means a convocation or an assembly. It designates the assemblies of the people, usually for a religious purpose. Ekklesia is used frequently in the Greek Old Testament for the assembly of the Chosen People before God, above all for their assembly on Mount Sinai where Israel received the Law and was established by God as his holy people. By calling itself "Church," the first community of Christian believers recognized itself as heir to that assembly. In the Church, God is "calling together" his people from all the ends of the earth. The equivalent Greek term Kyriak, from which the English word Church and the German Kirche are derived, means "what belongs to the Lord."