A ghoul is a creature (depending on mythology, either a demon or weak undead) that resides in a graveyard and consumes fresh corpses and unwary mourners. In times of famine, people may eat the remains of those who starve. For whatever reason, this may trigger the physical and mental degeneration of those who partake in human flesh; wether the meat is infected with a pathogen or such an act opens the door to possession, or some manner of spiritual "short circut"; the cannibal mutates into a hunchbacked, scrawny undead creature with a burning addiction to human meat.

When paired with the Fallout tag, however, Ghoul refers to a mutant strain of humanity with festering skin; created by massive radiation exposure.