Inclusions are clearly visible to the naked eye.
Slightly Included. Inclusions are easy to see under 10x magnification. Some are visible to the naked eye.
Very Slightly Included. inclusions are present, but hard to see under 10x magnification.
Very, Very Slightly Included. Inclusions are present, but extremely hard to see - even under 10x magnification.
Internally Flawless The diamond is internally flawless but has tiny external blemishes. Rare, hard to find, and beautiful.
Flawless. The diamond is flawless. Stones like this are extremely rare, expensive, and difficult to buy.
Most diamonds have imperfections in the form of internal flaws and surface blemishes. These imperfections are graded on a scale of FL (flawless) to I1-I3 (included). FL diamonds are the rarest and hardest to find.