Shapes
It's fairly common to confuse a diamond's cut with its shape. Shape refers to the overall outline of the diamond when viewed from the top. Round is the most popular diamond shape, followed by squared shapes such as princess, Asscher and emerald. Other shapes includes: Rectangular, Pear, Heart, Oval etc.

Cut
The cut of a diamond determines its brilliance. There is no single measurement of a diamond that defines its cut, but rather a collection of measurements and observations that determine the relationship between a diamond's light performance, dimensions and finish. Most gemologists consider cut the most important diamond characteristic because even if a diamond has perfect color and clarity, a diamond with a poor cut will have dulled brilliance. The width and depth can have an effect on how light travels within the diamond, and how it exits in the form of brilliance. There are various cutting styles, including Brilliant, Marquise, Emerald, Princess, Step and Mixed.