What is a Cabochon

The name Cabochon comes from the Middle French caboche (head). 
 A Gemstone Cabochon (often refereed to as cab) is a gemstone which has been shaped and polished as opposed to faceted, and it may have a flat bottom. 
The classical shape for cutting Gemstone Cabochons is an ellipse. However, shapes could be anything from round or circular to ovals, squares or rectangles and any free-form shape. 
Due to the fact that the eye is less sensitive to small asymmetries in an ellipse, as opposed to a uniformly round shape, such as a circle, an ellipse shape is more attractive looking.