NPS (Non-Player characters) are generally characters that exist to be used as plot devices. Most of the time, they are specified whether they are open or closes. NPCs serve as names to mention for the use of roleplays or characters used to further a roleplay.
Types of NPCs:
Locked NPCs-- Played only by admins for events and other nonsense.
Open NPCs-- Exist for plebeian use. Anyone may use an open NPC.