Diamond inclusions are internal flaws. Tiffany rejects any diamond with noticeable imperfections to the unaided eye.
FL
FL diamonds are Flawless
IF
IF diamonds are Internally Flawless
VVS1 VVS2
VVS diamonds (1 and 2) are Very, Very Slightly Included
VS1 VS2
VS diamonds (1 and 2) are Very Slightly Included
SI1 SI2
SI diamonds (1 and 2) are Slightly Included
I1 I2 I3
I diamonds (1, 2 and 3) are Imperfect
The gemmological standards in this section refer only to individually registered engagement diamonds set in certain ring styles.