Sounding familiar? Since the average of squared instantaneous voltages is in units of volts squared, taking the square root at the end (“root of the mean of the squares”) brings it on home.

More broadly, root mean square refers to a mathematical equation that's somewhat self-explanatory if you know what those terms mean, as it's the square root of a number set's mean square.

Then there was root-mean-square (RMS) voltage. For those nice sine waves, you took the peak voltage and divided by the square root of two, 1.414 or so. You know that kid in the front of the class?