A ghost is the spirit of a deceased person who, for one reason or another, was unable to move on to the next life and thus haunts their place of death. They can be good, bad or indifferent – largely determined by who they were in life and how they died.
Usually, they appear as they were in life and are often mistaken for living people. They can also appear in a wispy, distorted or flickering form. They are naturally intangible but can slam doors and throw objects around, and some ghosts have highly developed telekinetic skills. Ghosts are often seen carrying objects that were important to them in their lives and wearing clothes associated with the way they died (for example, a white dress for a Victorian murderer or a hat for a child who fell off a horse). They can be seen in places of natural darkness but can also be projected into light.
In medieval Europe, it was common for particular locations to be haunted. This is largely due to beliefs that ghosts were souls assigned to Purgatory, and that they visited the living to ask for prayers in order to end their suffering. It is also believed that ghosts can be demonic, and that they can tempt and torment the living.
When writing a ghost story, it is crucial to think carefully about your setting and how your characters might be affected by the presence of a ghost. This is particularly true if the ghost is potentially dangerous.