The 4 C's of jewelry are a set of criteria used to evaluate and describe the quality of gemstones, particularly diamonds. They stand for Cut, Color, Clarity, and Carat Weight:

Cut: The cut of a gemstone, particularly in the case of diamonds, refers to the way it has been shaped and faceted. A well-cut gemstone will have precise angles and proportions that allow it to reflect light and sparkle brilliantly. The cut is crucial in determining a gem's overall visual appeal.
Color: Gemstone color is assessed based on a scale. For diamonds, the scale goes from D (colorless) to Z (light yellow or brown). The presence or absence of color is a significant factor in a gemstone's value. Other colored gemstones, like sapphires and emeralds, are also graded on their specific color characteristics.
Clarity: Clarity refers to the presence of internal or external flaws, known as inclusions and blemishes, in a gemstone. Clarity grades range from Flawless (no inclusions or blemishes visible under 10x magnification) to Included (inclusions and blemishes visible to the naked eye). Higher clarity grades generally indicate a more valuable gemstone.
Carat Weight: Carat weight is a measure of a gemstone's size. One carat is equivalent to 200 milligrams. Larger gemstones are typically more valuable, but other factors like cut, color, and clarity also play a role in determining a gem's worth.

These four criteria are used to assess and communicate the quality and value of gemstones, particularly diamonds. By considering the 4 C's, you can make informed choices when purchasing or evaluating jewelry, ensuring you get the quality and appearance you desire.