Depth is the third dimension that differentiates form from shape.
Form is a three-dimensional object that can be constructed by two or more shapes.
Geometric Form is defined by its allegiance to mathematical construction.
Organic Form is defined by its simulation of natural substance.
Three-Dimensional is defined by an object or space having three coordinates: A width, a height, and a depth.
Volume is the amount of three-dimensional space a form occupies.