it represents your character afiliation to one of the 5 dark gods. if you check the skill page youll see the kills are grouped by god.
Khorne (battle skills)
Nurgle (Resistance and medic skills)
Slaanesh(diplomacy seduction agility)
Tzeentch( psy and knowleges)
now being affiliated to 1 particular god make a skill set able to be bought at a cheaper xp cost. but at the same time the oposite god skills become more expensive.
if you make a khorne melee warrior, it will be more cheaper xp wise, than making a tzeentch melee warrior. i would explain deeper but i am without sources at the moment.
your alignment is determined when you gain corruption points. again im sourceless at the moment. but if my memory is right it depends on those skills that are aligned to the gods. if you have more khorne skills at the moment you make a corruption test you are aligned to khorne.
