A circular revolving unit that is set into the floor, and which can turn mechanically to bring one set into view as another disappears, is a?

Answer: Turntable

Explanation:

Turntable is defined as the circular stage equipment that is used in the field of theatre. The major function of this stage is to control the rotating behavior of the floor or stage in mechanical manner.

Turntable is most commonly used in theatres, media, etc of the world. It is used for the purpose of changing the scene, shifting the background, rotation of floor disappearing the other scene etc.