A Ghost is a soul that has left the body due to death, yet remains trapped in the material world. Ghosts are liminal, that is, they are neither living nor dead.
The exact causes that create a ghost can be traced to the manner in which a person has died. Anyone might become a ghost after death, however people who die sudden and violent deaths are primary candidates for becoming ghosts. When death is sudden, the soul often does not even realize that the body has died and the ghost simply continues living the same routine it had when it was alive. When the death is violent, the tremendous fear which the human mind feels at the moment of death binds the ghost to the people and place it remembers in the last moment of life.
One way of dealing with a ghost is to appeal to a higher spiritual authority. Hanging a crucifix with holy water in your house will help to ward off potential hauntings. Though the ghost has influence over human beings, Christ has influence over the ghost. Another way of dealing with the ghost is to propitiate the ghost with small offerings. Build a small altar to the ghost and offer it candles and incense. This will help to pacify the malintent of the ghost.