Absidiole (semicircular chapel ©)

The translation in the title is followed by this sign ©; this means that it has been "invented" by me.

A semicircular chapelle (chapel), often attached to the chœur (choir) or the déambulatoire (ambulatory), sometimes built against the transept.
In plan (Wikipedia) the 3 chapels built against the déambulatoire are indicated in grey.
These particular chapels are also called chapelles rayonnantes (apse chapels). The bigger the church, the more apse chapels can be attached.
On the photograph the apse chapels of the Sacré-Cœur in Paray-le-Monial.
See also chapelle rayonante.

Absidiole

Sacré-Cœur - Paray-le-Monial