Poltergeist comes from German, with 'polter' translated as 'causing a disturbance,' and 'geist' meaning 'ghost,' so it is literally a ghost that causes a disturbance.
Accounts of poltergeists can be found in many different cultures and countries and date back as far as the 1st century. However, psychic researchers have attributed most reported incidents to be hoaxes, often perpetrated by adolescents (Wikipedia).
From the Web
"Poltergeist" on the Harry Potter Wiki