Mob

A Mob is any non-player character in an MMORPG, though generally the term refers to a generic, hostile NPC. The term is an acronym for Movable Object Block, which was another name for sprite, in the early days of computer color pixel graphics, which was the name of the technique used to have parts of the image move around on the screen independant of the background image. Although archaic for 3D graphics, the term has stuck, with people unfamiliar with (or new to) the art of programming trying to retcon their own ideas for the meaning.