What describes the explanation of symbols found on a ground plan?

The choice of "Key" accurately describes the explanation of symbols found on a ground plan because a key is used to provide clarification about the various symbols depicted in the drawing. It acts as a guide that helps everyone involved in the production understand what each symbol represents, such as different types of furniture, stage areas, or technical elements like lighting and sound equipment.

In the context of theatre production, a ground plan is a scaled diagram of the stage and its surroundings as seen from above. The key is essential because it allows directors, designers, and crew members to effectively communicate their vision and execute the production accurately, ensuring that all elements are placed as intended.

The other options do not fit this context. Set dressing refers to the items placed on the set to create a particular atmosphere or style but does not explain the symbols. Sight lines pertain to the visibility from various audience angles and would not describe the key to understanding the symbols. A wig is a costume accessory and also unrelated to the symbols on the ground plan.