In audio power, RMS stands for Root Mean Square, and it refers to the best value of the waveform. It is the measurement of continuous power that an amplifier can deliver. RMS only applies to AC signals.
RMS power is used in depicting the power of audio products. Power calculations are completed easily using RMS values since power, voltage and current for all AC circuits is given in RMS. However, calculation of RMS power vary with different companies, which sometimes makes it difficult to use RMS power to rate audio power. Another way to rate power is by using peak, or the highest voltage a waveform can reach.