180 degree rule

The 180 Degree Rule 

The 180 degrees rule in film making is supposed to help the viewer with their understanding of the Mise en sine in the picture. The rule implies that for example if you have two characters talking to each other then the camera can only record from one side of the scene.  

As this diagram below shows the camera can only stay on one side of the scene this prevents confusion among the viewers as the perspective would be wrong as it would look like the characters would be looking into space rather than at each other.
This is very important when we link it to editing as it allows the film to flow steadily and make it look like the two characters are talking to each other. It also allows a cut scene in between shot/reverse shots as the audience can fgure out which characters are where and when they are talking to each other.