au·di·to·ri·um / ˌôdiˈtôrēəm/ • n. (pl. -to·ri·ums or -to·ri·a / -ˈtôrēə/ ) 1. the part of a theater, concert hall, or other public building in which the audience sits.2. a large building or hall used for public gatherings, typically concerts or sports events. ∎ a large room for such gatherings, esp. in a school.