According to Wikipedia, Poltergeists are from German poltern, meaning to make noise, and Geist, meaning "ghost" or "spirit". They are ostensibly paranormal phenomenon attributed to an invisible spirit or ghost that manifests itself by moving and influencing objects, generally in a particular location such as a house or room or place within a house.
Poltergeists have been reported in many cultures, including India (where they are known as a Mumai), the United States, United Kingdom, Japan and Brazil.
While wikipedia says "Like the existence of ghosts in general, there is no credible scientific evidence for the existence of poltergeists" I beg to differ. There are many organizations committed to following and proving the existence of ghosts and paranormal spirits.