Poltergeist (from German poltern, meaning to rumble or make noise, and Geist, meaning "ghost", "spirit", or "embodiment") denotes a spirit or ghost that manifests itself by moving and influencing objects.
A pamphlet printed in London in 1698 by Mr. Ricard Chamberlain provides an account of a poltergeist-type haunting that had occurred some years before. Two copies of the pamphlet exist in the British Museum called: "Lithobolia, or stone throwing Devil. Being an Exact and True account (by way of Journal) of the various actions of infernal Spirits or (Devils Incarnate) Witches or both: and the great Disturbance and Amazement they gave to George Walton's family at a place called Great Island in the province of New Hampshire in New England, chiefly in throwing about (by an Invisible hand) Stones, Bricks, and Brick-Bats of all sizes, with several other things, as Hammers, Mauls, Iron-Crows, Spits, and other Utensils, as came into their Hellish minds, and this for space of a quarter of a year...."
Poltergeist activity originates with agents
Poltergeist activity tends to occur around a single person called an agent or a focus. Foci are often, but not limited to, pubescent children. Almost seventy years of research by the Rhine Research Center in Raleigh-Durham, North Carolina, has led to the hypothesis among parapsychologists that the "poltergeist effect" is a form of psychokinesis generated by a living human mind (that of the agent). According to researchers at the Rhine Center, the "poltergeist effect" is the outward manifestation of psychological trauma.
Poltergeists might simply exist, like the "elementals" described by occultists.
Another version posits that poltergeists originate after a person dies in a powerful rage at the time of death. According to yet another opinion, ghosts and poltergeists are "recordings." When there is a powerful emotion, sometimes at death and sometimes not, a recording is believed to be "embedded" in a place or, somehow, in the "fabric of time" itself. This recording will continue to play over and over again until the energy embedded disperses.
However some poltergeists have had the ability to articulate themselves and to have distinct personalities, which suggests some sort of self-awareness and intent. Practitioners of astral projection have reported the existence of unfriendly astral life forms, which Robert Bruce called "negs" (whom we might also identify with elementals). If they exist, these may well have the ability to affect the physical world.