Ghouls are not Ghosts and Ghosts are not Ghouls.  Many people combine these two types of Paranormal entities into a single description
...which is not correct.
You may ask...
What are the differences then?  
In terms of Folklore, Ghosts are the spirits of the dead.  We will delve deeper into exactly what this means in a future episode but for all intents and purposes, they are apparitions that may or may not be able to interact or communicate with the living.  They have no form, no mass, and are ethereal.
Ghouls, however, are usually associated with the undead (Zombies, Vampires and the likes).  It should be known that they are not technically undead creatures and should be more associated with demons or demonic creatures and in some cases, Jinn.  
In modern fiction, the ghoul is treated as an undead creature that consumes the dead (usually humans) and is often seen hanging around graveyards or places where it can feast on corpses.
Traditionally, the Ghoul comes from middle eastern, pre-Islamic folklore.  The first accounts of Ghouls are recorded from Ancient Egypt but there are additional accounts that go back to ancient Mesopotamia.