Diamonds are formed under extreme heat and pressure deep inside the earth and often display internal inclusions or external blemishes.
The clarity of a diamond refers to the absence of these inclusions and blemishes. The scale for grading clarity usually contains 11 grades starting with FL (flawless) and IF (internally flawless) followed by VVS1, and VVS2 (very, very slightly included), VS1 and VS2 (very slightly included), SI1 and SI2 (slightly included) and I1, I2 and I3, these are stones with quite noticeable inclusions often able to be seen with the naked eye.