Vi har detaljerade beskrivningar av alla tre i canon. De verkar likna på ytan, men de verkar inte ha mycket gemensamt (förutom en benägenhet för irriterande levande människor).
Ghouls
Från Fantastiska djur och var att hitta dem :
The Ghoul, though ugly, is not a particularly dangerous creature. It resembles a somewhat slimy, buck-toothed ogre and generally resides in attics or barns belonging to wizards, where it eats spiders and moths. It moans and occasionally throws objects around, but it is essentially simple-minded and will, at worst, growl alarmingly at anyone who stumbles across it.
Ghosts
Från Pottermore-post för spöken :
In the world of Harry Potter, a ghost is the transparent, three-dimensional imprint of a deceased witch or wizard, which continues to exist in the mortal world. Muggles cannot come back as ghosts, and the wisest witches and wizards choose not to. It is those with ‘unfinished business’, whether in the form of fear, guilt, regrets or overt attachment to the material world who refuse to move on to the next dimension.
poltergeists
Från Pottermore-posten för Peeves :
The name ‘poltergeist’ is German in origin, and roughly translates as ‘noisy ghost’, although it is not, strictly speaking, a ghost at all. The poltergeist is an invisible entity that moves objects, slams doors and creates other audible, kinetic disturbances.