Undead is, in popular culture, dead being that continue to act. Strictly speaking, the term refers to a reanimated corpse, usually by magic, like zombies and, extended sense, the spirits of dead people coming back as ghosts. The reanimated corpses still have the body, as opposed to the spirits, spooks and ghosts, which may be dead, but no longer have bodies , and are therefore perfectly intangible. There are undead of all types in most beliefs, which symbolic was taken to modern works. The undeads are also a popular theme novels and horror movies, and role playing. Vampires and zombies have seen a large body of literature and filmography devoted to them.
Most known novel is The Un-Dead by Bram Stoker, the original title of his novel Dracula, published in 1897.
The term undead refers to being immersed in an intermediate state between life and death, and still somehow in this precarious shape. The manifestation of the living dead can be through a physical body to a corpse, or that of an immaterial body, which is the case of ghosts and wraiths, which are persistent spirits of died people.
Same time, it is to differentiate two directions of undeads: some creatures are people previously living well, but fallen to the state of the undead after a particular event (vampires, liches, ghouls) while the others are dead people and then returned to life incompletely through magic (ghosts, mummies, skeletons). Note that the term zombie may designate a case as well as the other. However, strictly speaking, the definition applies only to resurrected dead (dead reverted partially live), immersed in a state of decay that makes them unaccountable for their actions. Living that are corrupt vampires and liches are more like demonic creatures because they have done a rite and made a pact with the occult powers knowingly.
The undeads do not feel pain, manifest supernatural powers (invulnerability to non- ritual attacks, insensitivity to fatigue), while their intentions are almost always hostile to the living. Vampires are well known to drink the blood of their victims to remain in a state of undead, the liche spread witchcraft, ghosts haunt the places of their past, and zombies eat human flesh .