180 degree rule, shot-reverse-shot and match-on-action

The 180° rule is a basic guideline in film making that states that two characters (or other elements) in the same scene should always have the same left/right relationship to each other. If the camera passes over the imaginary axis connecting the two subjects, it is called crossing the line. The new shot, from the opposite side, is known as a reverse angle.

Shot reverse shot (or shot/countershot) is a film technique where one character is shown looking at another character (often off-screen), and then the other character is shown looking back at the first character. Since the characters are shown facing in opposite directions, the viewer assumes that they are looking at each other.

Cutting on action or matching on action refers to a film editing technique where the editor cuts from one shot to another view that matches the first shot's action. Although the two shots may have actually been shot hours apart from each other, cutting on action gives the impression of continuous time when watching the edited film. By having a subject begin an action in one shot and carry it through to completion in the next, the editor creates a visual bridge which distracts the viewer from noticing the cut or noticing any slight continuity error between the two shots.

A variant of cutting on action is a cut in which the subject exits the frame in the first shot and then enters the frame in the subsequent shot. The entrance in the second shot must match the screen direction and motive rhythm of the exit in the first shot.