power level

Logarithm of the ratio of a power to a reference power. Levels are expressed in different ways: $L P = 1 2 ln ( P P 0 ) Np$ , where $Np$ is the symbol for the unit neper coherent with the SI, or $L P = 10 log 10 ( P P 0 ) dB$ , where $dB$ is the symbol for the unit decibel .

Source:

Green Book, 2nd ed., p. 79