Source: Pathfinder Bestiary, pg(s). 264
A poltergeist is a restless spirit of a mortal unwilling to move on from where it died and proceed to the afterlife. In contrast with ghosts, poltergeists are always evil and can manipulate physical objects through telekinesis.
Poltergeists are bound to a specific site and cannot travel far from it. Some are limited to a specific building, or even a single room. They are naturally invisible and only reveal their form to frighten interlopers; they otherwise use telekinesis to throw small physical objects, sometimes many at once.
Creatures who experience extreme emotional trauma before death might become poltergeists afterward, and disturbing a burial site — for instance, to construct a new building, even accidentally — often stirs them into creation.