Illustrated Architecture Dictionary
That part of a church between the sanctuary and the nave reserved for singers and clergy.
Chancel choir: The area of the church between a nave (or transept if there is one) and main apse. It is the area where the service is sung and clergy may stand, and the main or high altar is located.
Choir stalls: The benches in the chancel where the choristers are seated. Here, instead of facing east as the pews do in the nave, the choir stalls face north or south so that the choristers look across to each other.
Choir loft: A loft or balcony at the back of a church. A gallery occupied by the choir. The choir sits behind the congregation and faces the altar when they sing. In many American houses of worship, there is no choir in the chancel, but rather a choir loft. In many choir lofts, an organ console and pipes are located.
Choir is often spelled Quire in older books.
Examples from Buffalo architecture: