Non-corporeal invisible spirits of humans who died tragically or were murdered
Poltergeists are non-corporeal and invisible spirits of humans who have died a tragic death or were murdered in cold blood. So far as is known, all poltergeists were formerly human or at least half-human. They are only rarely encountered as a wandering monster but in such a case can be treated as a type 1 undead for purposes of turning or disrupting. More often, however, the poltergeist is in the area where it met its untimely end. The poltergeist's bond to this area is strong and turning is much more difficult, treat the poltergeist as a turning a type 3 undead in this case.
In combat, the poltergeist can only be struck by magical or silver weapons and its invisibility will cause all attacks against it to be made at -4 (unless the attacker can see invisible). It will not cross over sprinkled holy water, though after the holy water dries it is no longer effective at warding them. Holy water does not cause actual harm to poltergeists. A cleric can strongly present a holy symbol to keep them at bay as well, but again this does not harm the creature.
Poltergeists cannot physically attack. Instead they hurl objects with a telekinetic power at their opponents, attacking as a 5 HD mons
OSRIC