Note that slight inclusions are natural and quite common; perfectly flawless diamonds are extremely rare.

• F1 (flawless): Free from inclusions and blemishes
• IF (internally flawless): Free from inclusions; may have slight blemishes
• VVS1, VVS2 (very, very slightly included): Has minute inclusions or blemishes the size of a pinpoint when viewed through loupe
• VS1, VS2 (very slightly included): Has inclusions or blemishes smaller than a grain of salt when viewed through loupe
• SI1, SI2 (slightly included): Has inclusions or blemishes larger than a grain of salt when viewed through loupe. SI1 diamonds are usually eye-clean, which means the flaws can't be seen with the naked eye; SI2 stones may have visible imperfections
• I1, I2, I3 (imperfect): Has inclusions and blemishes that make the diamond look cloudy and lifeless