Clarity refers to the presence of inclusions in a diamond.
Inclusions are natural identifying characteristics such as minerals or fractures, that appear while diamonds are being formed. They may look like tiny crystals, clouds or feathers.
Inclusions are usually viewed at 10x magnification. The position of inclusions can greatly affect the value of a diamond.
Some inclusions can be hidden by a mounting, thus having little effect on the beauty of a diamond. An inclusion in the middle or top of a diamond could impact the dispersion of light, making the diamond less brilliant.
Inclusions are ranked on a scale of perfection known as the clarity scale. The scale ranges from F (Flawless) to I (Included) and is based on the visibility of inclusions at 10X magnification.