Undead

The undead are dead who can still interact with the Living. By the Third age, the term "Dwimerlaik" was used as a catchall term.

types

 * Barrow-Wights: not really undead, but evil spirits inhabiting the tombs of the Barrow-Downs. They often possess the grave-gifts and bones of those entombed there, making them sort of like the animate skeletons of other works.
 * Ghosts- the souls of the dead who are prevented from reaching their final reward. The largest concentration were the dead warriors of Rohan who betrayed Isildur and were cursed, haunting the mountain until Aragorn persuaded them to fight for him. Their faces often shift from skeletal frames to pasty shadows of themselves. Another great concentration were the Dead Marshes.
 * Nazgul or Ring-Wraiths: Formerly Kings of Men, the nine rings gifted to them by Sauron caused them to become ghost-like Wraiths who could only die if the One Ring were destroyed, or by technicality, such as fighting a woman. This is how the Witch-king was killed. if any warrior scored a hit, they were affected by the Black Breath, a magical affliction characterized by stygian despair. they cannot see properly, and rely on smell and hearing. However, wearing the One Ring allows the wearer to be "seen" by them. They carry swords meant to break off in the wound, and can turn the afflicted into a wraith.
 * Wraiths: people who have come into possession of a Ring of Power and wear it too long, or have been stabbed by a Morgul Blade. They are permanently invisible, and more or less immortal.