Space represents the area around an object, within an object or between objects. Space may give the illusion or effect of depth.
Positive space represents the subject of a piece. The area around objects may be referred to as negative space and acts as more than emptiness.
Negative space serves to balance and to highlight positive shapes.

Seven Elements of Design | eHow http://www.ehow.com/list_7676900_seven-elements-design.html#ixzz2T5Sc7j7i