Shape

"The infinite variety of lines" ultimately form shapes. Squares, circles, trapezoids, octagons, and so many more. One would define "shape" as the perceived area defined by borders, and/or color, that define the edge; we also know this as "form" We usually consider shape to be a 2D element, where when adding the words volume & mass, we instantly "see" it's 3D equivalent.

These shapes form positive and negative shapes, or figure and ground.  Positive shapes (figure) form the object clearly visible from the background. Negative shapes (ground), is the space between the figures and forms. Artists and Designers carefully and thoughtfully plan both of these for the final pictoral effect.

Distortion: 

Exaggerated shapes

 http://zainteriora.net/2008/01/17/carpets-of-rug-company/  

                 
                               

Curvilinear Shapes:

These shapes tend to be rounded and curved, that imply flowing shapes.

cited-

http://furniture.architecture.sk/2010/09/the-twist-chair-by-jonas-lyndby-jensen.php

Jonas Lyndby Jensen "Twist Chair"

Biomorphic Shapes:

These shapes are made of organic or natural forms.

                                                      cited

                                          http://www.cranbrookart.edu/Pages/3DDeptStu.html

                                        Cas Holman. Eco System 2005, Steel, Leather, Magnets