The 180-degree 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 angle. Reversing the angle is commonly thought to be disorienting and can distract the audience from the intent of the scene.
That said, there are ways you can break the 180 degree rule, and ways that you can bend the 180 degree rule.
This Video breaks down how to follow the 180 degree rule, how to break the 180 degree rule, and bend the 180 degree rule to achieve maximum effectiveness from your scene.
