NO = Normal Output fluorescent (can be T5, T6, T8, T10, T12 but normal output)

ODNO = Over-Driven Normal Output (hooking up a ballast in such as way as to over-drive the normal output bulbs, or by using a ballast such as an IceCap 430 or 660)

HO = High Output fluorescent (much of the T5 lighting being marketed in the hobby today is HO)

VHO = Very High Output fluorescent (these are T12 bulbs that run at 24"=75W, 36"=95W, etc.)

PC = Power Compact Fluorescent (this is basically a T5 lamp bent in half on itself; they come in both square-pin and linear-pin configurations)

MH = Metal Halide

Hope this clears up some of the confusion for you

-Jimbob