Proscenium

A proscenium is the architectural frame that separates a theatre stage from its audience. It often includes the opening through which spectators view the performance.

Proscenium arch: The arch or framed opening that separates a stage from the auditorium. It is the most visible architectural element of a proscenium.
House curtain: A curtain separating the stage from the auditorium, usually closed before a performance and during intervals. It can conceal the stage within the proscenium opening.
Teatro Olimpico: A Renaissance theatre in Vicenza, designed by Andrea Palladio and opened in 1585. Its permanent framed stage opening is an early landmark in proscenium theatre.
Thrust stage: A stage that projects into the audience, with spectators seated on three sides. It reduces the separation between stage and audience created by a proscenium.
Apron (theatre): The part of a stage extending beyond the proscenium arch toward the audience. It projects performance space in front of the frame.
Leg (theatre): A tall, narrow stage curtain used to mask the wings from the audience. Legs set the visible width of the stage behind the frame.
Teatro Farnese: A Baroque theatre built in Parma and opened in 1628, with a monumental proscenium arch. Its architecture helped establish the proscenium as a theatrical convention.
Arena stage: A stage surrounded by audience seating on all sides. It replaces the proscenium’s single framed viewpoint with views from every direction.
Backstage: The areas behind or beside a stage that are hidden from the audience during performance. It lies beyond the audience-facing boundary the proscenium establishes.
Sightline: An unobstructed line of view from a spectator’s position to a point onstage. The frame and auditorium layout must preserve useful views of the action.

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