Average power ratings for my Denon 8 Ohm rating is 110w, 20Hz-20kHz at less than .05% THD, with both channels driven, or 140w into 6 Ohms.
My Sony claims 110w at 8 Ohms but only at 1kHz and at 0.5%THD or 80w, 20-20kHz at 0.07% THD.
My ancient (1972) Kenwood at 8 Ohms is a whopping 18w, 20-40kHz at 0.5% THD.
Continuous average power is derived from the root mean square (RMS) of AC voltage and current and referring to it as "RMS watts", "RMS power", or "watts RMS" is incorrect. The correct term is "continuous average power", which is proportional to the RMS voltage. Of course, "RMS watts" or its variants, though technically incorrect, are in common usage: everybody uses it and most understand the general if not the specific meaning.