Clarity

A diamond's clarity is affected by any detectable external irregularities and internal imperfections created by nature when the diamond was formed. 
Imperfections such as spots or lines are called inclusions. The less inclusions, the higher the clarity and thus, the greater brilliance and ultimately, value. 
Inclusions can interfere with the passage of light through the stone, diminishing the sparkle and value of the diamond. 
According to the quality analysis system of the Gemological Institute of America, clarity is graded on a scale ranging from internally flawless (IF) to included (I). 
To be graded flawless, a diamond must have no inclusions visible to a trained eye under a 10x magnification in good light. 

The quality analysis system is as follows: 

FL, IF Diamonds: 
These Diamonds are the most rare and most expensive. These diamonds have been graded as (FL) Flawless: no internal or external flaws. (IF) Internally Flawless: No internal flaws. 

VVSI, VVS2 Diamonds: 
A superior quality diamond. Very, Very Slightly Included: Very difficult to see inclusions under 10X magnification. 

VS1, VS2 Diamonds: 
A lesser quality than the VVS1 or VVS2 grades. Very Slightly Included: Inclusions are not typically visible to the unaided eye, but are viewable at 10X magnification. 

SI1, SI2, and SI3 Diamonds: 
When combined with other factors, these grades represent good value. Slightly included: Inclusions are visible under 10X magnification, and may be visible with the unaided eye. 

I1, I2, and I3 Diamonds: 
These diamonds contain inclusions that are visible to the naked eye. I-grade diamonds are often purchased by customers seeking the largest stone possible for their money and these individuals are therefore not concerned about inclusions. However, Beifeld Jeweler's does not offer I3 grade Diamonds.