Clarity

Clarity is a key factor in determining a diamond’s value. Diamonds have internal features, called inclusions, and surface irregularities, called blemishes. Together, they’re called clarity characteristics. Clarity is the relative absence of clarity characteristics. Blemishes include scratches and nicks on a diamond’s surface. Inclusions are on the inside - tiny diamond or other mineral crystals which are trapped inside a diamond when it forms and might still be there after the stone has been cut and polished.
Like the color scale, clarity has a grading system, which describes the clarity which influences the diamond's value. Flawless diamonds are very rare and command top prices. At the other end of the scale are diamonds with inclusions that can easily be seen by the unaided eye. Between the two extremes are diamonds with inclusions visible only under 10X magnification. Some are difficult to see even then; others relatively easy.

The Clarity range:
FL – Flawless (no inclusions or blemishes)
IF – Internally Flawless (have some minor blemishes)
VVS1, VVS2 – Very Very Slightly Included (minute inclusions that are very difficult to see)
VS1, VS2 – Very Slightly Included (Some minute inclusions that are difficult to see)
SI1, SI2 – Slightly included (noticeable inclusions under 10X)
I1, I2, I3 – Included (large inclusions that may affect transparency and brilliance).