poltergeist, n.
A ghost that manifests itself by noises, rappings, and the creation of disorder.
Etymology [German: poltern, to make noises (from Middle High German boldern) + Geist, ghost (from Middle High German, from Old High German)]
According to some theories, poltergeists are forms of solid energy that are unconsciously controlled by a living person. In some cases extreme poltergeist activity is linked to demons. Ghosts and poltergeists display the same basic aspects (apparitions, strange sounds, smells, moving or vanishing objects, etc.). Ghosts are not violent, but poltergeists are. They can appear anywhere, build up to a climax and then start again. Poltergeists that reach the climax of their energy can be a danger to life. In extreme cases they bring both mental and physical affliction. If you meet one, be extremely careful.