180 Degree rule

In the example of a dialogue, if Ted is on the left and Bob is on the right, then Ted should be facing right at all times, even when Bob is off the edge of the frame, and Bob should always be facing left. Shifting to the other side of the characters on a cut, so that Bob is now on the left side and Ted is on the right, will disorient the viewer, and break the flow of the scene.
In the example of an action scene, such as a car chase, if a vehicle leaves the right side of the frame in one shot, it should enter from the left side of the frame in the next shot. Leaving from the right and entering from the right will create a similar sense of disorientation as in the dialogue example.