Ghouls were demons, a race of fallen Maiar, who were incorporeal and whose spirits took possess of bodies of dead Hildor (or more seldom Elves or even Orcs). The term Wight was often used synonymous with Ghoul, but was sometimes also applied to normal animated Corpses or spirits of dead Hildor.
The term Ghoul (Har.: "Gul") was common in Harad or southern Middle-Earth. In the Westlands a specific type of Ghoul known as the Gaunt-men were better known.Sometimes Ghoul was also used to designate mortals who, by some dark sorcery were able to stretch their natural lifespan, these would become what was known as "Ugûli" in the Black Speech, and were sometimes called "living Ghouls" (S."Dannath"), although their status as "alive" was debateable.
Use in MERP
In MERP the term "Ghoul" is often used to categorize creatures that have degenerated under the influence of evil, but have not yet died but stretched their lifespan in an unnatural way.By this definition the degenerated Stoor Gollum is labelled a Hobbit/Ghoul in several MERP Rulebooks.By this definition also other creatures as the Ring-Wights would fall into the "Ghoul" Category as would those evil Sorcerers and Vampires who used foul magic to artificially lengthen their lifespan.On the other Hand "Gul" is used in the MERP Books as a specific Haradaic word for a special class of demonic Undead.
In ROLEMASTER the term Ghoul' is commonly used for rotting corpses or specially deformed animated Corpses.The term Living Ghoul is used for beings that have been heavily tainted by the Unlife (in MERP the Ringwights, mannish Vampires, Gollum or Grima Wormtongue could be considered living Ghouls)