The church groundplan consists of the following fundamental elements:
Narthex – A low projection at the western end of a church, like a porch.
Nave – The main body of the church, the central approach to the high altar.
Side Aisles – Open area of a church parallel to the nave and separated from it by columns or piers.
Transept – An area set crosswise to the nave in a cruciform (“cross-shaped”) building
Chancel – The space around the altar in the sanctuary at the liturgical east end of a traditional Christian church building. It may terminate in an apse.
Choir – The area of the church between a transept and main apse. It is the area where the service is sung and clergy may stand, and the main or high altar is located.
Ambulatory – A semicircular or polygonal aisle. Often an ambulatory leads around the east end of the choir; separating the choir from apses or chapels.
This post on the pilgrimage churches describes the general development of the Romanesque groundplan.
Definitions are from the Glossary of Medieval Art and Architecture and Wikipedia.