What medieval Christian architectural feature is a long central hall of a church called?

The story behind the answer

It’s the main, central hall where the congregation gathers, running from the entrance (narthex) toward the crossing and chancel, often flanked by side aisles. That sets it apart from the choir (the clergy/chanting area near the altar), the transept (the crosswise arm), and the apse (the semicircular recess at the east end).

This space comes from the Roman basilica plan and became the dramatic focus of Romanesque and Gothic churches, lengthened and heightened with vaults and pointed arches to draw eyes and footsteps toward the altar. Its name traces to Latin navis, “ship,” reflecting an old metaphor of the Church as a vessel carrying the faithful through worldly tempests—a fitting image for processions, preaching, and the daily life of medieval worship.