Clarity of Diamonds

The clarity of a diamond describes the number and type of inclusions or imperfections present within it. 

The purer a diamond is, the higher its value. Most diamonds have very small inclusions. The fewer and smaller these inclusions are, the better the light can pass through the stone.

IF internally flawless no inclusions at 10x magnification
VVS1/VVS2 very very slightly included very, very small inclusions difficult to see under 10x magnification
VS1/VS2 very slightly included smaller inclusions difficult to slightly easier to see under 10x magnification
SI1/SI2/SI3 slightly included  small inclusions easy to very easy to see under 10x magnification
I1, I2, I3 included inclusions visible to the naked eye