A type jadeite jade: all natural jadeite, without any treatment. This type of jadeite jade can be bought as a real precious stone or investment.
B type jadeite jade: the natural jade is soaked in a mixed strong acid solution. Next, soak it in epoxy resin mixed with hardener. Then take it out and heat it to harden it. This kind of treatment can improve the color and transparency of the jade. But its texture is damaged and durability is greatly decreased.
Be aware that B type jadeite jade can also be called "natural color jadeite jade", because it is not dyed, its color is really natural. Ask the seller "is it soaked in acid solution?" as an additional question to confirm the jade you buy is an A type one.
C type jadeite jade: colored or dyed jade.
B+C type jadeite jade: the jade is dyed after acid-treated and resin-filled, which results in beautiful color and great transparency. But the color is not natural and the durability is greatly decreased.
D type jadeite jade: this kind is not real jadeite jade. It is another kind of jade or stone but looks like jadeite jade. It pretends to be jadeite jade because jadeite jade is the most precious and expensive one in the jade-like minerals.