Short answers, pulled from the story.
In folklore, a ghost is the soul or spirit of a dead person or non-human animal that some people believe can appear to the living. Descriptions vary from an invisible presence to wispy translucent shapes to realistic, lifelike forms resembling humans or animals.
According to a 2009 study by the Pew Research Center, 18% of Americans say they have seen a ghost. A 2005 Gallup poll found that about 32% of Americans believe in ghosts.
The overwhelming consensus of science is that there is no proof ghosts exist. Their existence is impossible to falsify, ghost hunting has been classified as pseudoscience, and there is no scientific evidence that any location is inhabited by the spirits of the dead.
The English word ghost comes from Old English gāst, meaning breath, spirit, soul, or ghost, which traces back to Proto-Germanic gaistaz. Linguists reconstruct that root from a pre-Germanic word meaning fury or anger, supported by links to Sanskrit hīḍ, meaning to be angry.
Skeptics such as Joe Nickell point to ordinary causes like air pressure changes slamming doors, humidity making boards creak, car lights reflected through windows, and pareidolia, the tendency to find patterns in random perceptions. Researchers have also linked ghost experiences to infrasound, geomagnetic field changes, sleep paralysis, certain drugs like zolpidem and diphenhydramine, and degenerative brain diseases such as Alzheimer's.
Spiritualism is a monotheistic belief system holding that the spirits of the dead can be contacted by mediums who relay information about the afterlife. It developed in the United States and peaked from the 1840s to the 1920s, with more than eight million followers in the United States and Europe by 1897.
Ancient cultures used sacrifice and magical banishment to prevent the return of the dead, including ritual feeding through events like the Chinese Ghost Festival and the binding of bodies before burial. The ancient Greeks held annual feasts to placate the dead, then firmly invited the family ghosts to leave until the same time the following year.