Clarity is an indication of a diamond's purity. Most diamonds contain tiny traces of minerals, gasses, or other elements that are almost always trapped inside during the crystallization process. These natural identifying characteristics, known as inclusions, are sometimes referred to as birthmarks. The "birthmarks" may look like tiny crystals, feathers, or clouds, and are what make each diamond unique. Most inclusions are not visible to the naked eye, so jewelers use a magnifying loupe to reveal any imperfections. The visibility, number and size of the inclusions determine a diamond's clarity. The fewer and smaller the inclusions, the more rare and valuable the diamond. Less than 1% of all diamonds are internally flawless (IF) and possess no inclusions.

The following are abbreviations for terms that are used worldwide to describe the clarity of a diamond:

IF, VVS1, VVS2: Internally flawless or near flawless. Impossible to extremely difficult to find any inclusions, even under 10x magnification. IF is "Internally Flawless," and VVS1 and VVS2 are "Very, Very Slightly Included."
VS1, VS2: 100% clean to the naked eye, and moderately difficult to very difficult to find inclusions with 10x magnification. VS1 and VS2 are "Very Slightly Included."
SI1, SI2, SI3: Should be completely to almost completely clear to the naked eye (eye clean) when viewed from the top. Fairly easy to find imperfections with 10x magnification. SI diamonds are "Slightly Included."
I1, I2, I3: Borderline "eye clean" to fairly easy to find imperfections with the naked eye. Very easy to find imperfections with 10x magnification. I1 through I3 diamonds are "Included."