What is an Proscenium arch?

A proscenium arch is an architectural element that forms the frame of a stage in a theatre. It is a large, arched opening that separates the stage from the audience, often decorated with elaborate mouldings and carvings. The proscenium arch creates a visual boundary between the real world of the audience and the fictional world of the stage, helping to suspend disbelief and immerse the audience in the performance