Drape set as masking piece at the side of the acting area. Usually set up in pairs across the stage and used in conjunction with borders to frame the audiences view. Apparently, the origin of the phrase "Break a Leg", meaning to take an extra encore from the legs after a successful performance.

Legs are tall, narrow drapes hung parallel to the proscenium at the sides of the stage. They're used to frame the sides of the acting space as well as to mask the wings, where actors and set pieces may be preparing to enter the stage.