Cut also refers to shape - round, square, pear, or heart for example. Since a round diamond is symmetrical and capable of reflecting nearly all the light that enters, it is the most brilliant of all diamond shapes and follows specific proportional guidelines. For example, the optimal table is between 55-60% while the optimal depth is between 58.5-62.5%. Ask a jeweler to find out more about these guidelines.
Non-round shapes, also known as "fancy shapes," will have their own guidelines to be considered well-cut.
The precision and delicacy with which your diamond is cut will determine its brilliance, its fire and its ultimate beauty. The shape you select is a matter of individual taste and today your choice is only limited by the skill and imagination of the craftsman. The round brilliant is the most popular shape, but there is a wide variety of others that range from the more traditional marquise, pear, emerald, oval, baguette, square or heart to the more fanciful and creative.
Radiant and Princess cuts for example which were introduced in the last few decades have grown in popularity and are a unique marriage between the cutter's art and modern technology.