Cut refers to the proportion and the arrangement of a diamond's facets, and the specific quality of the workmanship. Cut is the most important of the 4Cs because it determines the amount of brilliance, sparkle, and fire in a diamond.
A diamond that is “ideal cut” captures and releases the maximum play of light. Cut is the only “C” that humans can control.
In the vast majority of diamonds, color refers to the absence of color. With diamonds, the less color in the gem, the more valuable it is. While some of these subtle differences are not visible to the naked eye, they directly impact the quality and price of a diamond.
Clarity refers to the absence of inclusions and blemishes. The clarity grade is determined by the number, size, type, and location of inclusions. The fewer and smaller the inclusions, the less they interfere with light as it passes through the diamond. The highest graded diamond will be considered "Flawless."
Carat is the measure of a diamond’s weight (not size). A carat is 1/5 of a gram, and each carat has 100 points. Carat weight is the least important factor in determining the brilliance and beauty – and therefore the value – of a diamond. Two diamonds of equal weight can vary dramatically when one applies the other three Cs. That's why it's important to understand them all before you make your diamond purchase.