"Crossing The Line"

Violating the 180 degree rule is also known as "crossing the line". The rule states that the camera must stay on only one side of the subjects in a scene. An invisible line runs through the space of the scene.



Wikipedia writes: "This schematic shows the axis between two characters and the 180° arc on which cameras may be positioned (green). When cutting from the green arc to the red arc, the characters switch places on the screen."

Here's a YouTube video by Peter John Ross that shows how the rule works.