In architecture, the nave is central part of a church, extending from the narthex to the chancel and flanked by aisles outside the nave area. (Medieval Latin navis, from Latin, ship - probably from its shape.)
In a medieval cathedral, the nave was the area reserved for the non-clergy. There were no pews in the Nave, and on weekdays the large open area often served for the town marketplace, political meetings, places of various trades including, on some occasions, even that of prostitution.
Often smelling of animal dung and human urine, naves were not very clean places. Hence, altar screens were designed to separate the more sacred areas of the cathedral and keep out the unwashed and unholy.