Noun: An evil spirit or phantom, especially one supposed to rob graves and feed on dead bodies.
Ghouls originate from Arabic culture as vile beings looming around grave sites, or any other uninhabited areas. A male ghoul is referred to as ghūl while a female is called ghulah. They have a penchant for human flesh, and would lure their prey with trickery and deception (especially female ghouls). It wasn't until Antoine Galland translated One Thousand and One Nights into French that the western idea of a ghoul was introduced into European culture.
In most, if not all zombie fiction, ghouls and zombies are two different entities. However it was a nickname for Night of the Living Dead's zombie- briefly stated in a final report, declaring that a heavy blow to the head, or gunshot, would fell the 'ghouls'