1. The difference between a proscenium stage and a thrust stage is that the thrust stage extends out into the audience on three sides while a proscenium stage is all placed behind the proscenium arch.
2. A fly gallery is a catwalk that runs from the proscenium wall to the upstage wall where a pin rail sits that is used by the fly crew to control the entire fly system.
3. A scrim can be used in a variety of ways on the stage. It is a big piece of fabric that can either be opaque, transparent, or foggy to change the feeling of the scene. To make it opaque, everything behind it must be unlit and a light can be shined from above or from the sides. To make it transparent, if the scene behind it is lit but there is no light actually projected on the fabric. To create a foggy/dreamy look, the scene behind must be entirely lit.