Powered-Lift just means that they aren't using their wing surfaces for lift take-off/landing but are using them for lift during normal flight. They [edit:might] be able to auto-rotate down in the case of a powerplant failure just like a helicopter.
Here is the exact definition:
> (425) Powered-lift. A heavier-than-air aircraft capable of vertical take-off, vertical landing, and low-speed flight that depends principally on engine-driven lift devices or engine thrust for lift during these flight regimes and on non-rotating aerofoil(s) for lift during horizontal flight.
Here is the exact definition:
> (425) Powered-lift. A heavier-than-air aircraft capable of vertical take-off, vertical landing, and low-speed flight that depends principally on engine-driven lift devices or engine thrust for lift during these flight regimes and on non-rotating aerofoil(s) for lift during horizontal flight.