We don't use Grade system like AAA or AA... because sometimes a gemstone has a Good color (AAA) but minor cutting quality (BA)..or the oposite situation where the quality of the stone is medium (A) but very detail cutting (AAA). That's why we use "Stars" to describe the overall quality of our gemstone. where each property (color, Cutting, and clarity) has different stars. But.. in some of our products you might find that we still have been using the old grading system.
Which has comparison as follows :
AAA (A3) : 4 stars.
AA (A2) : 3 stars.
BA: 2 stars.
C : 1 star

Very exelent quality for beads standard
Very beautiful, but not the most popular color
Common as you will see in the market
Not constant color in one string.  Sometimes mixed color.
Good shape.  Cut beatutifully by machine.
Cut beautifully.  But the hole might not be straight or the hole edge might not be beautiful.
Not beautifully cut.  The shapes might not be very round or not be symmetrically.
Looks like cut by hand.
Very good
Not very good.  Contains a lot of inclusion.  Looks cloudy.

N Not enhanced. The stone has received no enhancement and the seller will provide a guarantee that there has been none.
B Bleaching: The use of chemicals or other agents to lighten or remove a gemstone's color.
C Coating: The use of such surface enhancements as laquering, enameling, inking, foiling, or sputtering of films to improve appearance, provide color or add other special effects.
D Dyeing: The introduction of coloring matter into a gemstone to give it new color, intensify present color or improve color uniformity.
F Filling: As a by-product of heat enhancement, the presence of solidified borax or similar colorless substances which are visible under properly illuminated 10X magnification.
G Gamma/Electron Irradiation: The use of gamma and/or electron bombardement to alter a gemstone's color; may be followed by a heating process.
H Heating: The use of heat to effect desired alteration of color, clarity, and/or phenomena. (Residue of foreign substances in open fractures is not visible under properly illuminated 10X magnification.)
I Infilling: The intentional filling of surface breaking cavities or fractures usually with glass, plastic, resin with hardeners and/or hardened foreign substances to improve durability, appearance and/or add weight.
L Lasering: The use of laser and chemicals to reach and alter inclusions in diamonds.
O Oiling/Resin Infusion: The intentional filling of surface breaking cavities with a colorless oil, wax, natural resin, or unhardened man-made material. (Oil, man-made resin, cedar wood oil, Canada balsam, paraffin, etc.)
R Irradiation: The use of neutron, requiring an environmental safety release from the Nuclear Regulatory Commission, with the combination of any other bombardement and/or heat treatment to alter a gemstone's color.
S Bonding/Stabilization: The use of colorless bonding agents (commonly plastic) within a porous gemstone to give it durability and improved appearance.
U Diffusion: The use of chemicals in conjunction with high temperatures to produce color and/or asterism-producing inclusions.
W Waxing/Oiling: The impregnation of a colorless wax, parafin and oil in porous opaque gemstones to improve appearance.
Category of synthetic stones
SYN Synthetic materials. The name synthetic must be accompanied by a specific reference to the actual composition.
IMIT Imitations, product-simulants, subsitutes. Trade names used to promote various simulant products in these category must be accompanied by a specific reference to the actual composition of the simulant.
ASBL Assembled materials, composite, doublets, triplets. Tag for products of multiple layers or combinations of manufactured and/or natural materials fused, bonded or otherwise joined together to increase stability and/or to imitate the appearence of a natural gemstone, create a unique design or generate unusal color combinations.

The above codes and explanations were taken from the American Gem Trade Association's AGTA Source Directory 2000-2001.