If you get the term RNP on the chart ie RNAV(RNP) RWY XX, it would most likely also state 'Authorisation Required' or SAAAR (old FAA term). These approaches are typically curved, sometimes in high terrain environments. They require authorisation for airline, aircraft type and crew and as previously stated, a Required Nav Performance which has to be met.
An RNAV on the other hand could be RNAV(GPS) or RNAV(GNSS) is your standard RNAV.