Cue – An act that a stage manager does to remind an actor of their line or an act that a stage manager does to tell the technical crew to perform a certain action. May be verbal of with an action.
Hot Spot – An area on the stage that is very bright because lights are pointed at it. It adds a sense of importance to the spot and to whatever actor may be occupying that space. Portrays importance to whatever/whoever is in the “Hot Spot.”
Sightlines – Lines that are imagined by the crew to determine where on the stage is visible to the audience, and where on the stage the view is blocked. Actors must be aware of these imaginary lines at all times or risk having the audience lose sight of an action done on stage.
The Fourth Wall – An imaginary wall put towards the front of the stage that the actors use to pretend as though the audience is not there, allows for no interaction between audience and actors.
Escape Stairs – Stairs that are out of sight from the audience and allows for the actors to move around on different levels of the stage without the audience realizing it. Portrays a lager sense of scene differentiation.
I like how you chose terms that describes the “invisible” actions or events that takes place during a place (even Hot Spot can be view by the audience as an invisible cue to direct their attention). Just a side note, not something of much importance, but I’m sure you mean “or” instead of “of” in the sentence of the first term, “May be verbal of with an action.”