No diamond is perfect under a magnified glass
Most diamonds contain some inner flaws, or inclusions, that occur during the formation process. The visibility, number and size of these inclusions determine what is called the clarity of a diamond. Diamonds that are clear are more brilliant, and thus are highly priced. The clarity grade is based on the size, number, position, color, and characteristics of the impurities, broken down into eleven grades from Flawless to Imperfect.
FL : Flawless , IF : Internally Flawless , VVS1 : Very Very Slightly Included 1 , VVS2 : Very Very Slightly Included 2 , VS1 : Very Slightly Included 1 , VS2 : Very Slightly Included 2 , SI1 : Slightly Included 1 , SI2 : Slightly Included 2 , I1 : Imperfect 1 , I2 : Imperfect 2 , I3 : Imperfect 3