group of people regularly attending a particular place of worship

A congregation is a group of people who have come together (congregated) for something, usually for religious worship. In Christian churches the word “congregation” is often used to mean all the people in the main part of the church, but not the choir or the priests. This term came from long ago after the church was first formed. For example: the order of service might say that the choir will sing verse 1 of a hymn and "the congregation are asked to join in at verse 2".