180degree rule.

180degree rule is a basic guideline of film making. It means when you have two people for example, facing each other, then there is an imaginary line running straight through them, and you can not 'cross the line'. As this would then make the people start facing a different way to what they were a minute ago, thus confusing the audience and the flow of the scene. E.G, Sam is facing left and Peter is facing right, if you swapped to the other side of them (crossing the line) Peter would be facing left and Sam would be facing right.