Undead

"Undead" refers to dead beings who could still interact with the living. By the Third Age, the Rohirric word Dwimmerlaik, meaning "spectre" or "work of necromancy", was used as an encompassing term.
== Types ==
* Barrow-wights were evil spirits inhabiting the tombs of the Barrow-downs. They often possessed the grave-gifts and bones of those entombed there, making them similar to the animate skeletons of other works.
* Ghosts (the Army of the Dead, specifically) were the souls of ones dead who were prevented from reaching ultimate rest. Gorlim the Unhappy might be considered one of these. The largest concentration were the dead warriors who betrayed Isildur, and whom he cursed, haunting the mountain until Aragorn persuaded them to fight for him.
* Nazgûl or Ringwraiths: Formerly kings of Men, the nine Rings of Power given them by Sauron caused them to become ghost-like Wraiths. They could not see properly, were permanently invisible and relied on smell and hearing. The Nazgûl carried daggers known as Morgul-blades meant to break off in the wound, which could turn the afflicted into a wraith. Frodo was stabbed by one at Weathertop. However, it is mentioned that Nazgûl are not properly undead.
* Phantasms were delusions and/or spirits or fallen Maiar and therefore not truly undead. Morgoth and Sauron used them for their treachery. It is said Saruman also used them.
* Lingerers were Elves whose bodies have been consumed by their fëa. To men, they were indistinguishable from bodiless spirits. These elven spirits were not really undead, because they were never dead to begin with.
* The "Houseless" were ghosts of slain Elves who were evil, hateful, or otherwise sinful in life and defied the call of Mandos. These Elven ghosts had the unique ability to possess living things; most often they desired to steal the bodies of Men to become material again, but according to some, they also could possess anything alive. Old Man Willow may have been possessed by one of the Houseless.
There may also have been some form of undead residing in the Dead Marshes.