Final answer:
The term for the area behind the choir or high altar of a large church is the apse. It's typically a semicircular or polygonal area at the east end of a church, near the chancel and distinct from the nave or aisles, which are other elements of church architecture.
Step-by-step explanation:
The term for a separate division behind the choir or high altar of a large church is apse. In the context of church architecture, the apse is often a semicircular or polygonal area, sometimes domed, at the eastern end of a cathedral or church. The choir area, which the question mentions, is the space in a church where the choir sings and is part of the chancel, located near the altar. This space is separated from the main body of the church, known as the nave, which is the central and primary part of the church stretching from the main entrance to the steps of the chancel. On the other hand, an aisle refers to the side spaces alongside the nave, usually separated from the central space by columns or piers, allowing for movement around the outer edges of the church.