Poltergeist is indeed a German word, a compound formed from the words "poltern" (meaning "to knock" or "to make noise") and "geist" (meaning "ghost" or "spirit"); it literally means "noisy ghost".
Poltergeist is a German word, and it is used mainly in literature dealing with paranormal phenomena to talk about a spirit (Geist) which makes noise (poltern) or moves objects.
