When we talk about form in art, what are we talking about? Resource: http://char.txa.cornell.edu/language/element/form/form.htm
Shape and form are two elements of art that are closely related to one another. Shape is what defines the two-dimensional area of an object, whereas forms are objects that are three-dimensional, having length, width, and depth. For example, a square is a shape, but a cube is a form. A triangle is a shape; a pyramid or a cone is a form. When one draws an apple that in nature is a form, one draws a shape that represents the apple. If one creates an apple out of clay, that clay apple is a form. In a two-dimensional artwork, an artist may try to create the illusion of form through the use of shading, foreshortening, perspective, and other techniques.
I added in some things about shape just to clear things up, hope it helps.