opera house
A theater designed for live opera before an audience, usually with substantial backstage space and an orchestra pit.
An opera house is a theater designed for the performance of operas in front of an audience. It normally has an especially large backstage area for opera sets and staging, and an orchestra pit in front of the stage. Many opera houses have capacity for hundreds or a few thousand audience members.
The stage and supporting spaces are designed for opera production. A venue that merely accommodates an occasional concert performance of an opera need not have this purpose.
An ordinary theater or symphonic hall has a different principal design purpose. The production requirements distinguish the opera house from those related performance spaces.