A ghoul is described as an ugly creature that resembles a slimy, buck-toothed ogre. They tend to live in the attics or barns of wizards and witches. They are relatively harmless creatures but are just seen as nuisances because of the noises they make by groaning and throwing objects. They are relatively dimwitted and live off of bugs and other household pests.
Under the Department for the Regulation and Control of Magical Creatures there is The Ghost Task Force. The Task Force is summoned to remove unwanted ghouls from houses that have passed in to Muggle ownership.
There is also a Chameleon Ghoul. A special type that can disguise itself as any everyday object to avoid detection.