The 180′ rule is a big part in the filming process. It is a rule saying that a camera should be placed somewhere inside 180 degrees on a particular side of the invisible line of a shot containing two people filmed in a sequence. However, if the camera crosses this imaginary line, there is confusion for the audience. This is because, it makes it look like the two people are switching positions.
Here are some diagrams:
In this diagram, if the camera crosses over into the red zone, it almost “reverses” the view of the two people; which means that it looks like the actors have switched sides compared to the green zone.
In the film ‘Whiplash’ a 180 degrees rule is shown. This is because, the camera does not cross over the line. We can see this because, the characters do not switch sides.