What are the drapes that curtain off the sides of the stage referred to as?

The correct answer is "legs." In theatrical terminology, legs refer to the vertical drapes or curtains that are used to mask the sides of the stage. Their primary function is to prevent the audience from seeing backstage areas and to create a more focused viewing experience. Legs can also help in shaping the stage's visuals by allowing light to be directed onto the performance area without distraction from what is happening offstage.

Understanding the purpose and position of legs is vital in stage design and production, as they play a critical role in the overall aesthetic and practical aspects of a performance. The terms related to the other options—wings, backdrops, and flies—pertain to different elements of stagecraft. Wings are typically the spaces adjacent to the stage for actors and props to enter and exit; backdrops are large, painted or printed scenes that serve as a background for the action; and flies are ropes used in rigging systems to move items in and out of view above the stage. Each has its distinct purpose, separate from the function of the legs.