The diamonds Clarity refers to how clean a diamond is. Diamonds have imperfections which are present in its rough state. The clarity scale is used to measure how great those imperfections or "inclusions".
Clarity is determined using a very complex method of determining the size, location, and visibility of inclusions.
The Clarity Scale is a follows:
Shows no inclusions or blemishes of any sort under 10 x magnifications when observed by an experienced grader.
Have no inclusions when examined by an experienced grader, but will have some minor blemishes.
VVS1, VVS2 - Very Very Slightly Imperfect:
Contains minute inclusions that are difficult even for experienced graders to see under 10x magnification.
VS1, VS2 - Very Slightly Imperfect:
Contains minute inclusions such as crystals, clouds or feathers when observed with effort under 10x magnification.
SI1, SI2 - Slightly Imperfect:
Contains inclusions such as cavities, knots clouds, feathers and included crystals which are noticeable to an experienced grader.
I1, I2, I3 - Imperfect:
Contains inclusions such as large feathers or large included crystals, which are obvious under a 10x magnification and may affect transparency and brilliance.