Flawless (FL) - Shows no inclusions or blemishes under a 10x magnification when observed by an experienced grader.
Internally flawless (IF) - Shows no visible internal inclusions, but may have minor surface blemishes visible when using 10x magnification.
Very, very slightly included (VVS1 or VVS2) - Minute inclusions that are difficult for even an experienced grader to see under a 10x magnification.
Slightly included (Sl1, Sl2, Sl3) - Refers to diamonds which have small inclusions that can be easily located using a 10x microscope.
Imperfect (I1, I2, I3) -Contains very obvious inclusions that can usually be seen with the naked eye.