The "4Cs of Diamonds" refer to the four key factors that determine a diamond's quality and value: Carat, Cut, Color, and Clarity. Carat measures the weight of the diamond, with one carat equal to 0.2 grams. Cut describes how well the diamond has been shaped and faceted, affecting its brilliance and sparkle. Color assesses the presence of any color in a diamond, with the most valuable diamonds being colorless. Lastly, Clarity evaluates the presence of internal or external flaws, known as inclusions and blemishes, respectively. Together, these factors help buyers understand a diamond's overall quality.