THE SHAPE 
SHAPE:
 It is the external appearance of an object or element in a image.
NATURAL SHAPE :
They are the ones related to nature. They haven't been created by any human.
ARTIFICIAL SHAPES/FREE FORMS:
They are  shapes that have irregular profile or silhouettes as well as their inner surface. Organic shapes whose are usually natural even though they are sometimes unusual. 
GEOMETRIC SHAPES:

 Shapes whose parts follow a mathematic order, laws or pattern.

FLAT SHAPES:

 They have two dimensions such us a paper sheet, a cinema screen or a canvas.

FORM: 

They are volumetric shapes, they appear and are three dimensional.