RNP5 is required navigation performance grade 5. Further info, see:
http://www.eurocontrol.int/cns/cns_annex2.html
B(asic)-RNAV defines European RNAV operations which satisfy a required track keeping accuracy of ±5NM for at least 95% of the flight time. This level of navigation accuracy is comparable with that which can be achieved by conventional navigation techniques on ATS routes defined by VOR/DME, when VORs are less than 100 NM apart.
For further info, see:
http://users.forthnet.gr/ath/mpang/whatis.htm