Faction is how the NPC's of the world rate you. You can find out how you stand with a particular NPC by right-clicking them or targeting them and using the hotkey for the '/consider' command (the default is 'c').
- Glares at you threateningly and Scowls at you ready to attack are both considered KoS.
- Merchants will only trade with you if you are Apprehensive or above in faction. Otherwise they will tell you "I will not deal with one such as you!"
This term is also used to refer to the relationships between groups of NPCs. Many of the world's NPC's are associated with a particular faction with which you can gain or lose favor. Many quests require a certain level of faction with the quest initiator or specific NPC factions. Favor is typically lost with a faction by killing NPCs aligned with it. Killing NPCs that are opposed to that particular faction or performing quests for NPCs of that faction may increase a player's favor with them. It is almost always easier to lose favor with faction than it is to gain it. The amount of faction gained or lost by performing acts that affect the faction is not directly apparent to players; it can only be determined by trial and error.