*auditorium*

n. [ L. See Auditory, n. ] 1. The part of a church, theater, or other public building, assigned to the audience. [ 1913 Webster ]

☞ In ancient churches the auditorium was the nave, where hearers stood to be instructed; in monasteries it was an apartment for the reception of strangers. [ 1913 Webster ]

2. a building, or a room within a building, containing a large open space for public gatherings, and often having a raised stage where speakers or presentations may be easily viewed by the audience. The students assembled to hear the president speak in the auditorium. [ PJC ]