What is apron for in theater terms?

The apron is the area of the stage that extends beyond the proscenium arch (the arch that separates the stage from the auditorium). It traditionally was used for musicians and other performers who were not part of the main action on stage. The term comes from the fact that this area was often covered by a curtain, much like an apron that covers a person's lap.

In modern theater, the apron may be used for various purposes, including extending the stage area for performances, accommodating actors who are seated, or providing a place for the audience to interact with the actors during interactive or immersive performances.