180 Degree Rule / Match on Action (Match Cut)

The 180 Degree rule is the movment of which the camera can move to a certain point of only to the 1 side of the scene, basically meaning that there is a "imaginery line" that goes straight across the scene of which the camera cannot cross as this will then create confusion as the characters will be looking the other direction. The only way of beng able to do this however would be the move the camera constantly to the other side rather than just cutting there

http://video.google.co.uk/videosearch?q=180+degree+rule&hl=en&emb=0&aq=f#

Match Action is the simultaneous movemnt between one camera shot to another, but with the same movment of character taking place. This if done well will not be noticable to the viewer as shoulder flow from shot to shot without anymovments missed by the camera.

http://video.google.co.uk/videosearch?q=180+degree+rule&hl=en&emb=0&aq=f#q=match%20cut&hl=en&emb=0