There are 6 schools of magic, 3 for human and 3 for mags. And the style of the school is the main charasteristc, which can be Fire or Air for BoneCrushers, Shadow or Light for Dodgers and Earth or Water for Heavyweights.
The weapons from lvl11 gives +magic damage, and both weapons and armors give resist ,example
bonecrusher resist heavyweight, Dodger resists bonecrusher schools magic. You can also get rings/amulets to wear that increase you resistance to all schools. i prefer Shadow school because primary spells cause extra "poisoning" that can't be removed with dispel.