The raw material differet, different tensile strengths, weaves, different numbers from manufacturers and all that, but really it isn't much of an indication of quality.
A lot of crap frames will "up spec" their materials to get some perceived quality, or the highest quality frames use it as well!
At the end of the day how it is glued together (the quality of the resins, layup, R&D in to what needs to go Where - and why) that makes more difference.
(For instance someone like Cyfac use T800, T1200 is 50% stronger Fibre, yet Cyfac are most likely the best carbon frames in the world)
T 1200HM/ M30 HM-3K TWIL
I am not 100% sure but T1200 (Toray 1200, which is their highest tensile rating), HM (High Modulas) / (or) M30 (Mitsubishi 30 ton rating) - 3K TWIL ( is the weave 3000 fibres in a twill pattern 2 up two down diagonally across) remembering that 1 fibre is about 1/50 of a human hair!
BTW 90% of all carbon comes form those 2 manufactures!