A mob, mobile, or monster is a computer-controlled non-player character (NPC) in a computer game such as an MMORPG or MUD. Depending on context, every and any such characters in a game may be considered to be a "mob", or usage of the term may be limited to hostile NPCs and/or NPCs vulnerable to attack. Common usage refers to either a single character or a multitude of characters in a group as a mob. In most modern graphical games, "mob" may be used to specifically refer to generic monstrous NPCs that the player is expected to hunt and kill, excluding NPCs that engage in dialog or sell items or who cannot be attacked. "Named mobs" are distinguished by having a proper name rather than being referred to by a general type ("a goblin," "a citizen," etc.). "Dumb mobs" are those capable of no complex behaviors beyond attacking or moving around.
Mob (video gaming) Wikipedia
Defeating mobs may be required to gather experience points, money, items, or to complete quests. Combat between player characters (PCs) and mobs is called player versus environment (PvE). PCs may also attack mobs because they aggressively attack PCs. Monster versus monster (MvM) battles also take place in some games.
A game world might contain hundreds of different kinds of mobs, but if players spend a certain amount of time playing, they might become well aware of the characteristics presented by each kind and its related hazard. This knowledge might dull the game to some extent.
The term "mob" is short for "mobile," which was used by Richard Bartle for objects that were self-mobile in MUD1. The term as it exists in MMORPGs is derived from the MUD usage. (Source code in DikuMUD uses the term "mob" to refer to a generic NPC; DikuMUD was a heavy influence on EverQuest.) The term is properly an abbreviation rather than an acronym, but backronyms for "MOB" such as "mobile object," "monster or beast," "mere ordinary beast" and "mean old bastard" have also been coined.