MOB

A MOB also known as a Monster, is an NPC, that can be attacked throughout normal game play. These creatures give experience, guild experience, and loot to the players as the player plays the game.

The term MOB is a rather archaic reference to 'mobile' or any form of mobile or living creature. Why we use it to refer to monsters, creatures, humanoids... that's not particularly clear, except that there's not many better choices.

Monster Object is why we call it a mob, generally.