The 180 degree rule

The 180 Degree Rule

This photo shows the basics of the 180 degree rule, the pictures of the people correspond with what the camera near it will see.
The 180 degree rule is a rule that states that if you are filming something you cannot cut to a shot past the 180 degree rule, because this puts people on different sides and makes the shot disorienting  and confusing to watch, for example we see the man in green on the left of the image, whether he's facing the camera or not, he's always on the left, if you pass the 180 degree line he moves over to the right of the frame and that's confusing for the viewer.
You can pass the 180 degree line as long as you show the transition, for example showing the camera moving over the line with a pan or track, we then see and understand that we're on the other side of the line and know what's going on.