A ghost is an alleged noncorporeal manifestation of a dead person (or, rarely, an animal or object). It is often thought to be the spirit or soul of a person who has remained on Earth after death. According to some sources, a ghost may be the personality of a person after his or her death, and not tied directly to the soul or spirit. Every culture in the world carries stories about ghosts, but they vary across time and place, with disagreements both as to what ghosts are and whether they are hallucinations or a part of nature.

Beliefs about ghosts

Ghosts are often depicted of a human size and shape (although some accounts also mention animal ghosts), but typically described as "silvery", "shadowy", "semitransparent", or "fog-like." Ghosts do not have a gross physical body like human beings, only the subtle astral body. Sometimes they do not manifest themselves visually but in terms of other phenomena, such as the movements of an object, spontaneous throwing of a light switch, noises, etc., which supposedly have no natural explanation.

In the West, those who believe in ghosts sometimes hold them to be souls that could not find rest after death, and so linger on Earth. The inability to find rest is often explained by unfinished business, such as a victim seeking justice or revenge after death. Criminals sometimes supposedly linger to avoid Purgatory or Hell. It is sometimes held that ghosts reside in Limbo, a place, according to nonorthodox Catholic doctrine, between Heaven and Hell where the souls of unbaptized infants go. It is worth noting that while mainstream Protestants and Evangelical Christians believe in the existence of principalities, they do not believe in ghosts (as spiritual manifestations of the dead) and would generally attribute more violent ghosts, such as poltergeists, to the actions of demons.

Some ghost researchers approach the possibility of ghosts from a more scientific standpoint, seeking to find correlations and causal relationships between recordable phenomena and the supposed presence of ghosts. Those who follow this approach most often believe that ghosts are not actual disembodied souls or spirits, but rather they are impressions of psychic energy left behind by a deceased (or in some rare cases, still living) person. They assert that traumatic events (such as a murder or suicide) cause mental energy to be released into the world, where it may be experienced by other people who are sensitive to its presence. This way of thinking classifies ghosts in the same category of preternatural unexplained phenomena as poltergeists/telekinesis, ESP, and telepathy. Theories from this approach often encounter difficulties in explaining ghosts that appear to be sentient, such as those which answer questions or react to specific actions from people present. However, it may be possible that enough of a dead person's psyche might be imprinted on an environment so as to give the likeness of thought or autonomy.

In Asian cultures (such as China), many people believe in reincarnation. Ghosts are those souls that refused to be "recycled" because they have unfinished business, similar to those in the West. Exorcists can either help a ghost to be driven away or reincarnated. In Chinese tradition, apart from being reincarnated, a ghost can also become immortal and become a demigod, or it can go to hell and suffer for eternity, or it can die again and become "ghost of ghost". The Chinese also believe that some ghosts, especially those who died of drowning, kill people in order to rob them of their rights to reincarnation. The victims of such paranormal "murders" are called ti4si2gui3 (???), literally "substitute death ghost" or "substitute devil" which in Chinese is a synonym for scapegoat. Also in China, particularly in Guang Zhou area the Chinese people usually hold a Chinese version of Day of the dead ritual for their ancestors in Autumn. The ritual consists of burning Hell Bank Notes and other luxury items made of paper mache as well as pouring wine three times on their grave and leaving food. An older ritual is for the living family to prepare a grand feast for their dead relatives "returning" home. During the time of feast, those relatives amongst the living are not allowed to leave their bedrooms regardless of how much noise the ghost makes.

Very detailed information about ghosts is given in Garuda Purana, a scripture from Vedic (Hindu) tradition.

Both the West and the East share some fundamental beliefs about ghosts. They may wander around places they frequented when alive or where they died. Such places are known as "haunted"; the rounds they go on are known as "hauntings". They often wear the sort of clothing in which they would have been seen when alive.

Buddhist Samsara includes the concept of the Hungry ghost realm. Sentient beings in that realm are referred to as Hungry Ghosts because of their attachment to this world. Asuras are also referred to as "fighting ghosts".