Proscenium

 
The proscenium is the part of a modern theatre stage between the curtain and the orchestra. A Proscenium theatre is a theatre space whose primary feature is a large frame or arch (called the proscenium arch even though it is frequently mistakenly called the prosecnium.) So the word proscenium is often misused by performers, even designers, who refer to the 'proscenium' when they actually mean the proscenium arch.