In electrical engineering, an effective value (RMS, abbreviation for Root Mean Square) is the quadratic mean value of a physical quantity that changes over time, such as an alternating current or an alternating voltage.
The effective value Ueff of an alternating voltage is the voltage constant in time which delivers the same energy as the alternating voltage at an ohmic resistance R in a representative time.
The effective value Ieff of an alternating current is the current constant in time which delivers the same energy as the alternating current at an ohmic resistance R in a representative time.