Congregation - A group of people who adhere to a common faith and habitually attend a given church.

A congregation is the group of members who make up a local Christian church, Jewish synagogue, or other religious assembly. It also means those who are present at a service thereat, as opposed to the building itself. (wikipedia)

A group of Christians that meet and worship together, usualy having a formal organization and a church building. Congregational denominations are run as an alliance of Congregations, the national organization being seen as a way to pool resources and present a unified message to the unbelieving world.