Undeath is a mythological, legendary and fictional condition in which a deceased being behaves as if alive. One who suffers from undeath is called an undead. Many times, even when referring to a single undead being, the collective term "the undead" will be used, especially with creatures like zombies where their individualism has become murky or non-existent.
A common example of undead is a corpse re-animated by supernatural forces with the application of the deceased's own life force or that of another being (such as a demon). Undead may be incorporeal like ghosts, or corporeal like vampires and zombies. The undead are featured in the belief systems of many cultures, and appear in a great number of works within fantasy and horror fiction.
Bram Stoker considered using the title The Un-Dead for his novel Dracula (1897), and use of the term in the novel is mostly responsible for the modern sense of the word. The word does appear in English before Stoker but with the more literal sense of "alive" or "not dead", for which citations can be found in the Oxford English Dictionary. Stoker's use of the term refers only to vampires, and the extension to other types of supernatural beings arose later. Most commonly, it is now taken to refer to supernatural beings which had at one time been alive and continue to display some aspects of life after death, but the usage is highly variable.