One of the first things we do when we’re constructing a show is to break the story down into “French scenes”, like this.
A “French scene” is generally defined as beginning with the entrance of a character, and concluding with a character’s exit — so each French scene is a unit among a particular group of characters. Let’s say there was a section of the play which started with Kelly and Rikki talking; Woodchuck and Mouse enter and join the scene; and then Rikki exits, leaving Kelly, Woodchuck and Mouse onstage concluding the scene. You really have three “French scenes” here: Kelly & Rikki; Kelly, Rikki, Woodchuck & Mouse; Kelly, Woodchuck & Mouse. Usually the energy level or direction of a scene changes with each character’s entrance or exit (or at least it should.) Sometimes we’re a little broad in our definition of a “French scene” but usually for us it means one tight, discrete dramatic unit.