Non-Player Characters, or NPCs, generally refer to non-hostile creatures not controlled by a human player.
Technically speaking, NPCs can actually include both friendly and hostile characters. Though in practice players tend to use the term "Mob" or "Monster" to refer to hostile NPCs/creatures, and not really care about the superset of hostile and non-hostile characters.
Usually, non-hostile NPCs involved in combat (attacking or being attacked) are considered to be allies (even if they don't show up under the "Allies" section of the Party window), although it is not always the case. Most service-providing NPCs (collectors, merchants etc) are not considered allies.
For a complete list of all non-hostile NPC's in the game, see: Category:NPCs
All of the NPCs in the game (friendly, hostile and those that are both) can be found within the species of the Bestiary.
 NPC sub-types
The following are some of the more commonly found NPC types:
- Collectors (List) (Category)
- Merchants (Category)
- Tamers (Category)
- Skill Unlocking NPCs
- Guild NPCs
- Various NPCs:
See Category:NPCs by type for a more complete list.