Form refers to three dimensional objects. While shapes have two dimensions (height and width), forms have three dimensions (height, width and depth).
The overall unity of the visual elements in an artArt refers to a diverse range of human intellectual and expressive activities and the outcomes of those activities. Within this context art is further defined... work; it is usually contrasted with content. Form is sometimes used to refer to the three dimensional aspect of an art work, as opposed to shapeShapes are two-dimensional. Positive shapes represent solid objects and negative shapes show the surrounding space. Geometric shapes are perfect and regular. Organic shapes are irregular..., which is seen as referring to two dimensional aspects.