A term used for many things. (1) A game system and series of individual games published by White Wolf. (2) A term for the gamemaster used in White Wolf and other games. (3) One of the four Blacow Player Types which was adopted by Robin Laws for his seven player types.

References:

• Robin's Laws of Good Gamemastering(approve sites)
• Player Types (from Glen Blacow and Robin D. Laws)