Which of the following is used to describe a curtain that often blocks off the backstage area from the audience?

The correct term to describe a curtain that blocks off the backstage area from the audience is "tormentors." Tormentors are vertical curtains or panels that are positioned to either side of the stage and help to conceal the backstage area from the audience's view. They play an important role in the overall aesthetics of a production by creating a polished appearance and maintaining the illusion of the performance.

Other choices refer to different types of stage curtains or elements. Teasers, for instance, are horizontal drapes that are used to mask the top of the stage or to set the overall height of the proscenium. Legs are also vertical curtains, but they are specifically designed to frame the sides of the stage and typically do not block the backstage area completely. The grand drape, also known as the main curtain, is the large curtain that hangs at the front of the stage and is typically used to open and close the show. Each of these elements serves unique functions in stage design, but tormentors are specifically intended to separate the backstage from the audience, making them the correct answer.