A chapel
A small church that is not a parish church. It may be part of a larger entity such as a hospital, school, or an alms-house, or it may stand alone.
An enclosed part of a church with its own altar.
on the curved back wall of the choirIn a church with a cruciform floor plan, the part of the church that lies on the side of the nave opposite to the transept. The main altar is in the choir.. In the symbolism of the cruciform floor plan, in which the choir stands for the head of the crucified Jesus, these chapels form, as it were, a halo around this head. This accounts for their name: ‘radiating chapels’.