A Poltergeist (German word meaning "Noisy Ghost") are a more rare form of haunting. They are a ghost/spirit that seemingly come out of nowhere and are intent on expressing themselves by causing a lot of chaos. They have been known to move objects around, stack items, throw things, etc. A poltergeist can last days, weeks, months or years. They go as suddenly as they come.
In many cases, however, another explanation was found...a human explanation. Seems that in many reported cases, there was a teenage girl involved, and they were indirectly causing the activity with their mind and had no idea.