A ghost is said to be the apparition of a dead 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 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 odors."

Ghosts are a controversial anomalous phenomenon. According to a poll conducted in 2005 by the Gallup Organization, about 32% of Americans believe in the existence of ghosts. The term ghost has been replaced by apparition in parapsychology, because the word ghost is deemed insufficiently precise.

The belief in ghosts as souls of the departed is closely related to the ancient concept of animism, which attributed souls to everything in nature, including human beings, animals, plants, rocks, etc.

Although the human soul was sometimes symbolically or literally depicted in ancient cultures as a bird or other animal, it was widely held that the soul was an exact reproduction of the body in every feature, even down to clothing the person wore. This is depicted in artwork from various ancient cultures, including such works as the Egyptian Book of the Dead, which shows deceased people in the afterlife appearing much as they did before death, including the style of dress.