The term 'AREA BEHIND AN ALTAR' can be summarized as the APSE, which is a four-letter word. An APSE is a semicircular recess in the wall of a church, typically at the east end, containing the altar and often having a vaulted roof. It is usually found in traditional Christian churches, such as Roman Catholic, Anglican, and Eastern Orthodox. The APSE is often used to house the choir and the clergy, and it is also used for special ceremonies.