Negative space is a compositional tool used in both two- and three-dimensional work. The simplest way to describe it is as: "space where other things are not present."

Negative space has no "negative" connotation. It's actually a wonderful, if often neglected, design element. Properly used (as with Henry Moore's sculptures, or Zen brush paintings, or even your basic Rorschach test ink blots), it is just as important as what is there.