The 180-degree rule

 The 180-degree rule is when the camera has to remain on the same side of an imaginary line which is perpendicular to the cameras view point, from which the shot is taken. Two people or objects should always face or move the same way to avoid viewer being disorientated.

i found this information below on the internet to help further explain the 180-degree rule

The 180° rule is a basic film editing guideline 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.

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.