RNAV is a form of navigation based on waypoints and GPS position. It stands for Radial Navigation.
RNP corresponds to Required Navigation Performance, and basically corresponds to the degree of certainty associated to the real geographical position of the aircraft VS the position shown on the aircraft's instruments through inertial systems of GPS. RNP1 means the aircraft's real position is within 1nm laterally of the position shown on the aircrafts instruments, and likewise for RNP2, etc.