The difference between open negative space and closed negative space is very straightforward. Open negative is where you have negative space around four sides of a subject. No part of the subject touches the edge of the canvas or paper. There is "empty" space all around it.
Closed negative space is where the subject stretches across the composition to touch the edge. Part of the subject closes off a part of the negative space, turning it into a smaller shape. When planning a composition, the shapes and lines of closed negative spaces need to be taken into consideration, not only those in the subject itself.
