The 180° rule is a cinematography guideline that states that two characters in a scene should maintain the same left/right relationship to one another. When the camera passes over the invisible axis connecting the two subjects, it is called crossing the line and the shot becomes what is called a reverse shot.
Cutting on action or matching on action refers to film editing and video editing techniques where the editor cuts from one shot to another view that matches the first shot's action. A common example is a man walking up to a door and reaching for the knob.
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.
