It basically describes playing style. Insofar it is a very individual understanding of your respective character.
A paladin would be a warrior, which does no evil deeds, and uses magic only to heal or protect, and would wield a sword as main weapon.
A barbarian would also be a warrior, wielding axe or mace, and not using magic at all.
A Nercromancer would concentrate his magic skills in the art of conjuring.
Or any other combination and/or restriction you can think of. The main point is to remain consistent throughout the game, which in DD requires a lot of self discipline.
