A qualified personal residence trust (QPRT) is an irrevocable trust to which a donor (the "grantor") makes a gift of a personal residence (usually) for the ultimate benefit of the grantor's immediate family, typically the grantor's children.
The Treasury Regulations under IRC 2702 explain that the personal residence transferred to the QPRT must be the "principal residence" of the grantor or one "other residence" of the grantor and that the residence may not be used for something other than a personal residence when it is not occupied by the grantor.