The "4Cs of diamonds" refer to the four key factors that determine a diamond's quality and value: carat, cut, color, and clarity. The carat measures the diamond's weight, with larger stones generally being more valuable. The cut describes how well the diamond has been shaped and faceted, affecting its brilliance and sparkle. Color assesses the presence of any hues in a diamond, with colorless stones being the most sought after. Lastly, clarity evaluates the presence of internal or external flaws, known as inclusions and blemishes. Together, these four characteristics help buyers choose the perfect diamond.