Over the Shoulder Shot (OSS)
This shot is framed from behind a person who is looking at the subject. The person facing the subject should usually occupy about 1/3 of the frame.
This shot helps to establish the position of each person, and get the feel of looking at one person from the other's point of view.
It's common to cut between these shots during a conversation, alternating the view between the different speakers.
In older 4x3 framing, the person facing away from the camera would typically be cut off just behind the ear. In 16x9 and other widescreen framing, there is more width available and more of this person can be shown (as above).
This shot can be varied quite a bit to include the shoulder or back of the person facing the subject.