180 degree rule (180-degree line)

The 180-degree rule, or 180-degree line, is a screen direction camera operators follow for easy viewing. The 180-degree rule is an imaginary line or axis where the action in a scene occurs (e.g., between two principal actors in a scene), and the camera must not cross over that line. Otherwise, there is a distressing visual discontinuity and disorientation. This is similar to the axis of action, an imaginary line that separates the camera from the action before it, and filmmakers should not cross.