A basilica is a large, rectangular building with a central nave and side aisles, often used as a public meeting place or for religious worship.
An apse refers to a semicircular or polygonal recess at the end of the nave in a basilica, typically housing an altar.
A transept refers to an area that intersects with and crosses over the main axis (nave) of a basilica, forming the shape of a cross.
The nave is the central part of a basilica where people sit or stand during religious services. It runs from the entrance to the apse.