The 4 C's:
Cut - Describes the finish, proportion and polish of the diamond. These factors determine the fire and brilliance of a diamond.
An Ideal Cut diamond is a round (also known as brilliant) or princess cut diamond that is cut to ideal proportions and angles and has excellent polish and symmetry ratings.
A True Hearts diamond is a round or princess cut diamond that exhibits a near flawless Hearts and Arrows pattern of perfect optical symmetry, maximizing the diamond’s fire, brilliance and light dispersion.
Clarity - Describes the clearness or purity of a diamond. A grade is assigned to each diamond, with "F" representing a flawless diamond to "I" describing a diamond that has inclusions. Most diamonds can be found at various grades between “F” and “I.” Diamond buyers will sometimes choose a gem with some inclusions, as long as they are not visible to the naked eye.
Color - From white to yellow, diamonds receive a grade for the amount of color they contain. Diamond buyers prefer colorless to near colorless diamonds, with diamonds graded J, K, and L offering the best value for a customer’s money.
Carat - Carat refers to the weight of the diamond. One carat is equivalent to 0.20 grams. The larger the carat, the pricier the diamond, although the other "C's" can influence the final price significantly.