RMS voltage stands for Root Mean Square voltage, which is defined as the square root of the mean square of instantaneous values of the voltage signal. It is a measure of the effective or average voltage of an AC waveform. The RMS voltage is also known as the equivalent DC voltage because the RMS value gives the amount of AC power drawn by a resistor similar to the power drawn by a DC source.
For a continuously varying voltage, the RMS value is most important in the case of an AC signal because the instantaneous value of an AC signal varies continuously with respect to time, unlike a DC signal, which is relatively constant. The RMS voltage of a sinusoidal source of electromotive force (Vrms) is used to characterize the source. It is the square root of the time average of the voltage squared. The value of Vrms is V0/√2, or, equivalently, 0.707V0, where V0 is the peak voltage.
In summary, RMS voltage is a measure of the effective or average voltage of an AC waveform, and it is calculated as the square root of the mean square of instantaneous values of the voltage signal.
