A skeleton is a type of physically manifested undead often found in fantasy, gothic, and horror fiction, as well as mythology, folklore, and various kinds of art. Most are human skeletons, but they can also be from any creature or race found on Earth or in the fantasy world.
Animated skeletons in The Dance of Death (1493), a woodcut by Michael Wolgemut, from the Liber chronicarum by Hartmann Schedel.
José Guadalupe Posada's 1913 La Calavera Catrina zinc etching
A CG art skeleton, as commonly found in modern fantasy-theme games.
The undead are beings in mythology, legend, or fiction that are deceased but behave as if alive. Most commonly the term refers to corporeal forms of formerly alive humans, such as mummies, vampires, and zombies, which have been reanimated by supernatural means, technology, or disease. In some cases, the term also includes incorporeal forms of the dead, such as ghosts.
The Ghost of Barbara Radziwiłł by Wojciech Gerson. Ghosts are a common form of the undead.
The Dead Lovers, ca. 1470 (Strasbourg, Musée de l'Œuvre Notre-Dame)
Utagawa Yoshiiku, Specter frightening a young woman