IF – Internally flawless – Cut gem: It means the stone is devoid of any visible inclusion with 10X magnification.
VVS – Very Very Slightly included. It means the stone has few inclusions, but visible under 10X magnification.
VS – Very slightly included – It means the stone has very few inclusions, but difficult to see face up. However, if looked more carefully or with a 10X magnification, one would be able to see these inclusions.
SI – Slightly included: The inclusions are clearly visible under 10X magnification and sometimes to the naked eye, but not affecting the brilliance.
I – Inclusions are clearly visible to the naked eye and it impacts beauty and brilliance of the stone.
I2 – I3 – Inclusion significantly impacts brilliance making the stone more suitable for cabochon.
Test
1 × $1.00 
2.60 carats Parti Brownish Green Sapphire
1 × $3,250.00