The second value of voltage is the actual useful voltage that is available and is called RMS. This stands for Root Mean Square and it is the standard way of measuring and reporting alternating current and voltage. It is not the peak; it is the average.

RMS Graphic

The RMS is found by dividing the peak amplitude by the square root of 2 (approximately 1.414). This yields the actual, useable voltage. It is typically represented by a dotted line drawn across each peak near the 70 percent point.