proscenium:  the metaphorical vertical plane of space in a theatre, usually surrounded on the top and sides by a physical proscenium arch (whether or not truly “arched”) and on the bottom by the stage floor itself, which serves as the frame into which the audience observes from a more or less unified angle the events taking place upon the stage during a theatrical performance. The concept of the fourth wall of the theatre stage space that faces the audience is essentially the same.

Ref: ESI

Source: Italian

Plural: Bokkadopri


Small scene used as background behind an opening such as a door or window in a larger stage scene.

Source: Sicilian

Plural: Fundali


Intermezzo: A light dramatic musical or other performance between the acts of a play; A short connecting instrumental movement in an opera or other musical work.

Source: Italian

Plural: Intermezzi