Ghost

A ghost is the spirit of a deceased humanoid. This type of undead is incorporeal in nature and only vulnerable to conventional weapons on the Ethereal Plane. A Ghost Brute is a ghost of an animal, plant, or magical beast that is stuck to the material plane.

A ghost is a creature on two planes, the material and the Astral Plane. A ghost's connection to the material plane is severed when you destroy it, but in a few days the ghost will usually come back. Ghosts are a repetitive nusance for those who live in one's particular haunt.

A ghost can also be under the control of wizards, sorcerers, liches, etc. In this case the ghost is finally put to rest when destroyed on material plane or the master of the ghost is dead. This is usually uncommon though, because to raise a ghost uses a lot more magic than raising a regular undead. A ghost's weapons usually consist of whatever weapons they carried in their mortal life and maybe a spell or two if they were a wizard or sorcerer, which is not the same as a lich.