rms is the power an amp can put out for an extended time. It is also the only power rating that really matters. Amps will say like 800 watts peak 400 rms. rms is what matters. youll get 400 watts. Usally like sony amps and cheap stuff have their peak ratings on them, not their true rms ratings. That amp i bet you don't even get half that power. Personally save your money and don't buy that amp. I agree buy cheap buy twice unless maybe ebay used.