Final answer:
The center circle part between the stage and seating area in a theater is called the orchestra or orchestra pit, which can be covered to serve as an apron for plays without musical accompaniment.
Step-by-step explanation:
The center circle part between the stage and the seating area in a theater is called the orchestra. This term has its origins from Greek theatre, where the orchestra was the circular dancing place situated in front of the stage. In modern theaters, the equivalent space is often referred to as the orchestra pit, and is the area below the stage level where the orchestra plays during a musical performance. However, during plays without musical accompaniment, this space can be covered and becomes additional space for the actors, known as the apron, which extends from the proscenium arch towards the audience.