What's the difference between ghosts and ghouls?

This two words have same initials and even the first three letters, "Gho", both refer to a kind of spirits. What's the difference between ghosts and ghouls?

Ghost-A ghost is said to be the apparition of a deceased person, frequently similar in appearance to that person, and usually encountered in places he or she frequented, or in association with the person's former belongings. The word "ghost" may also refer to the spirit or soul of a deceased person, or to any spirit or demon. Ghosts are often associated with hauntings, which is, according to the Parapsychological Association, "the more or less regular occurrence of paranormal phenomena associated with a particular locality (especially a building) and usually attributed to the activities of a discarnate entity; the phenomena may include apparitions, poltergeist disturbances, cold drafts, sounds of footsteps and voices, and various odours."

A ghoul is a monster from ancient Arabian folklore that dwells in burial grounds and other uninhabited places. The English word comes from the Arabic name for the creature: ghūl, which literally means "demon". The ghul is a devilish type of jinn believed to be sired by Iblis.

Ghoul- Ghul is also the name for a desert-dwelling, shapeshifting demon that can assume the guise of an animal, especially a hyena. It lures unwary travellers into the desert wastes to slay and devour them. The creature also preys on young children, robs graves, and eats the dead. Because of the latter habit, the word ghoul is sometimes used to refer to an ordinary human such as a grave robber, or to anyone who delights in the macabre.