GNSS is simply the generic term (Global Navigation Satellite System) for any satellite navigation system such as GPS, GLONASS, Galileo, etc.
My comment was more specific. ICAO defines two different RNP approach procedures: RNP APCH and RNP AR APCH.
In the US, RNP APCH is charted as
RNAV (GPS). Internationally, RNP APCH is charted as
RNAV (GNSS).
RNP AR APCH is usually charted
RNAV (RNP) everywhere.