2 measurements of power, actually both are in watts, rms is continuous power, like average power la, and then the other is peak or maximum power.
the following taken from bcae1.com........
RMS & Continuous Power output
CONFUSION:
Many people wrongly believe that the RMS power rating is the same as a continuous power rating.
Power:
First, power is a 'snapshot' of the amount of work being done at any point in time. It has no specified time component.
Ratings:
There are a lot of different ways to rate an amplifier's output power capabilities.
# A few possible ways to rate amplifiers: Watts (not much information and lends itself to many different interpretations)
When manufacturers state the power output in 'watts' (and only 'watts' i.e. 50 watts), they want you to assume that the wattage rating is an accurate measurement of the amplifiers ability to do a given amount of work (driving your speakers). In reality, the power rating could be derived by using peak voltage instead of the more honest RMS voltage when plugging the numbers into the formula P=E^2/R. This would give a power output/rating that's TWICE the RMS power output. Actually they could be using virtually anything to derive this vague specification (pulling a number out of thin air comes to mind).
# Peak watts (misleading because many will take it as a true measure of the work that the amplifier will do when driving the speakers)
If the manufacturer specifies wattage as 'peak power' they may say that they aren't trying to mislead their customers, but I believe that that is precisely what they are trying to do. They assume that the vast majority of people are going to accept the wattage as the maximum power that the amplifier can produce. If they use peak voltage to derive the peak power, the power specification may be legitimate but it is misleading. The peak power is mathematically twice the RMS power output.
# RMS watts (Better than peak power but it also lends itself to misinterpretation because it contains no specified element of time)
RMS wattage is an accurate way to measure power but the amplifier may only be able to produce the RMS voltage into the given load for a fraction of a second. The, less than honest, manufacturer may plug this RMS voltage into the P=E^2/R formula and give this number as the amplifier's output. If they give this as the power output of the amplifier but don't tell you that the amplifier can't continuously produce this power level, they are again misleading you.
# RMS continuous watts (the best, most accurate, honest way to measure power output)
When manufacturers rate their amplifiers at a given number of RMS watts continuous power output. They are using RMS wattage (derived from RMS voltage) which is the most accurate way to state the useful power produced by the amplifier. There is only one way to interpret this. They are also stating that the amplifier can produce the power continuously. If they didn't specify continuous power they may be trying to cover up the fact that the amplifier could only produce the RMS voltage required to drive the given load to a given RMS power for a fraction of a second (like in the previous example). When they state continuous output power, they are saying that the amplifier can easily and continuously produce the rated output power.
