A term used for mobs in a dungeon which are not a Boss Monster, and generally easy to dispatch relative to the difficulty of the dungeon. They are typically viewed as an annoyance by players, since they are the tedious and time-consuming preamble to boss fights.
However, killing trash mobs does have its benefits. They award a small amount of reputation, if applicable to the dungeon. In Molten Core, the trash mobs drop materials necessary for crafting fire resistance items, as well as two of the eight Tier 1 set pieces (the bind on equip wrist and belt pieces). In Zul'Gurub, killing trash mobs awards coins and bijous.