A mob is a type of non-player character (NPC) or monster in a computer role-playing game (especially MMORPGs). Mob is not to be confused with MOB (more often considered an acronym of Movable Object Block, a term for any on-screen moving object, or sprite, stemming from its use in the earliest text-based multi-user dungeons (MUDs)). There appears to be some debate on the exact origins of the term mob and its relation to MOB only makes things murkier.

The most commonly-held belief about the origin of the name is that in many early MUDs, there were three basic structures in the game: rooms, objects and mobiles; the latter being objects that can move, i.e. they are mobile, they can be attacked and thus removed from the game, which can be aggressive (may attack the player), and which wander through rooms when permitted. Because they are mobile, mobile was the term used to describe them. This term was later replaced by NPC to cover a broader spectrum of mobiles (dialog or quest, vendor, trainer and now mob, to name a few).

Backronyms such as "monster or beast" and "mere ordinary beast" have been developed. Another suggested origin is that mob is derived directly from (NPC); the letters M, O, and B respectively precede N, P, and C in the alphabet.

Killing mobs can give such rewards as experience points and items. Usually the combat is player initiated, however, if the mob is flagged as aggressive, it is configured so that it will challenge a player who enters within a certain range. This area is known as the aggro range or "aggro radius". A player engaged by such a mob is said to have aggro. This marks that player as the primary target of the attacking mob(s). Combat between players and mobs is called player versus monster (PvM) or in a broader sense, player versus environment (PvE); as opposed to player versus player (PvP) battles where the emphasis is on defeating an opposing player. Monster versus monster (MvM) battles, though rarer, may also exist.

Usage in MUDs (multi-user dungeons)

The term Mobile was originally coined by Richard Bartle in a paper describing an early MUD which was being constructed as a research project at the University of Essex. Although it originally referred to an object that could move (as opposed to one that couldn't), one reviewer of the paper misunderstood the term to be a reference to the classic children's toy or sculpture that goes by the same name - and referred to it as "an incredibly beautiful analogy to those hanging toys, which appear to move around randomly as if alive, while in fact being composed of mechanical parts and operating in accordance with fixed scientific laws". (Bartle was also suitably impressed by the analogy, and wished he'd thought of it.)

Other MUDs and MUD-like software use a variety of terms to describe these as objects, emitters, and actors.

Usage in MMORPGs

Mobs in MMORPGs usually refer to the generic monstrous NPCs that the player is expected to hunt and kill rather than NPCs that engage in dialog or sell items. Elite mobs, as in the game World of Warcraft, are special rarer monsters that are tougher than their regular counterparts and usually have better loot. Named mobs are distinguished by having a proper name rather than being referred to by their mob type (goblin, citizen, etc.) and are often key to the objective of missions or quests. Boss mobs are mobs of unusual power, often the most powerful foe in a defined area. Boss mobs are usually also named mobs, and vice versa. Farming is the repetitive killing of one specific mob type (usually well below the capability of the player) for the purpose of gathering large quantities of a specific resource dropped as loot by that type. Farming can also be used for the gaining of in-game experience points and/or valuable loot or money. This type of farming is known as grinding due to the tedious process of repeatedly killing mobs in one area. The mobs used for this type of farming are usually much tougher or easier depending on said mob.

Computer and video game gameplay | Mob | Competitive computer and video gaming