Where the carrier leases only the aircraft (without crew, insurance or anything else).
The distinctions are becoming meaningless anyhow as more and more financial organizations and lessors are working with airline customers to develop custom-made packages so the carrier gets exactly what it needs (any combination of Aircraft, Crew, Maintenance, Insurance).
For instance, an existing A340 operator might sign a lease for a few more A340s that covers the aircraft and maintenance only if the engine type isn’t the same in order to avoid the additional expenses of supporting a new engine manufacturer.