Few things in nature are absolutely perfect. THat's as true of diamonds as anything else.
Diamonds have internal features, called includsions, and surface irregularities, called blemishes. Together, they're called clarity characteristics.
Clarity is the relative absence of inclusions and blemishes.

Clarity Grade

Inclusions are enclosed within a gemstone. They might also extend into the diamond from the surface.

Blemishes are confined to the gemstone's surface.

 FL  No inlusions or blemishes of any kind when examined under 10X magnification by a skilled grader.
 IF  No inclusions when examined by an experienced grader using 10X magnification.
 VVS1, VVS2  Contain minute inclusions that are difficult even for experienced graders to see under 10X magnification.
 VS1, VS2  Contain small or minor inclusions observed with effort under 10X magnification.
 SI1, SI2  Contain inclusions that are noticeable to an experienced grader under 10X magnification.
 I1, I2, I3  Contain inclusions that are obvious under 10X magnification.

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