wat does ex dc and do stand for?

I'm going to take a wild guess and say you're looking at Sigma lenses.

EX is their designation for their professional line of lenses
DC is their designation for lenses sized specifically for APS-C or smaller sensors (i.e. not designed for use on film, full size sensor or aps-H size sensor cameras)

DO is a canon term:

DO — stands for Diffractive Optic and is used on Canon lenses which utilize a unique diffraction grating to control chromatic aberration and reduce lens size and weight.