A scrim is a type of
sheet used in theatrical
scenery. Scrims are hung vertically, with one side towards the audience. When lit from the front, they appear to be solid. When lit from behind, they are nearly transparent.
They were used to great effect in a recent URI production of Neil Simon's Brighton Beach Memoirs. The scenery crew built a house on stage. Downstairs, there were a few rooms and doors and such, and upstairs were two bedrooms. At the start of the show, the walls between the bedrooms and the hallway appeared to be wallpapered. Whenever a character would walk through the hallway, though, the lights in the hallway itself would fade up, lighting the scrim from behind, so the audience could see through the wallpaper. It was really a striking effect.