Which term is used to describe the imaginary line that determines the depth of the stage?

The term that best describes the imaginary line determining the depth of the stage is the plaster line. This line is crucial in stage design and blocking as it runs parallel to the proscenium arch, marking where the stage’s scenery meets the front opening. The plaster line helps creators delineate the area where the audience can see the performance, aiding in spatial orientation and ensuring that actors and set pieces are positioned accurately in relation to the audience's perspective.

The proscenium refers to the architectural elements framing the stage and does not specifically indicate depth. The center line is a vertical line that divides the stage into left and right halves, providing a reference for staging but not for depth. The downstage line generally relates to movement toward the front of the stage but does not define the overall depth in the same way the plaster line does. Understanding these terms is essential for effective stage management and design.