A stage in which the performance space sticks out into the house and the audience is seated on three sides

a performance space in which the audience is seated in a circle around the stage

Another version of Theatre in the Round but on a much larger scale

a form of theatrical stage in which the audience is predominantly on two sides of the stage, facing towards each other

a stage where the audience views the action only from the front of the stage

the structure in the front of the stage that frames the action of the play. It can be squared, arched, and the stage curtain is generally behind it. 

the invisible barrier that separates the stage from the audience and through which the audience watches the action 

The backdrop or "drop" is a large drapery of painted canvas that provides the rear (or upstage) masking of the set

Legs are vertical curtains used to hide the "wings" (backstage area) from view and frames the audience view of the stage

A curtain used to define the top limit of the stage and to mask or hide lights and unused scenery and curtains 

A gauzy and translucent curtain. It may be plain or painted. When the light is thrown on the front of it, it becomes opaque. 

Another name for a Border curtain. It often refers to the to the first masking curtain on stage 

A decorative, narrow curtain hung along the top of the proscenium arch on the side towards the audience

Solid white curtain at the rear of the performance area used to represent the sky, time of day, distant areas, or to create unique lighting affects. 

A tubular metal bar, sometimes known as a pipe, from which overhead lighting instruments, backdrops, and scenery can be attached to or hung

The portion of the stage that extends beyond the proscenium opening

This is where an orchestra will usually be placed in a musical production. It generally extends across the breadth of the stage and gets it's name from the fact that it is lower than the stage-- so the musicians don't block the audience's view

Where the audience sits during the performance 

The areas on either side of the stage that the audiences does not normally see

A hallway behind the masking curtains to allow performers and technicians to move from one side of the stage to the other without being seen 

These directions are from the actors' perspective looking out towards the audience