FL : Flawless – No internal or external imperfections visible using a 10X microscope.
IF : Internally Flawless – No visible internal imperfections, but may have minor surface blemishes visible when using a 10x microscope.
VVS1-VVS2 : Very, very slightly included – Inclusions that are extremely difficult for a skilled observer to locate using a 10x microscope.
VS1-VS2: Very slightly included – Very small inclusions that are very difficult for a skilled observer to locate using a 10x microscope. In rare instances, with larger stones, some VS1/VS2 inclusions can be seen with the naked eye, after first being located using a microscope.
SI1-SI2 : Slightly included – Refers to diamonds which have small inclusions that can be easily located using a 10x microscope. In some instances, such inclusions can be seen with the naked eye, after first being located using a 10x microscope.
I1-I3: Imperfect – Medium to large inclusions which are readily apparent to a skilled observer with the unaided eye.
A carat is a unit of measurement and 1 carat is equal to 200 milligrams or 0.2 grams. Hence a 1.25 carat diamond will weigh 250 milligrams.