For an electric circuit, it's a complex number with real part equal to the resistance and imaginary part equal to the reactance.
For an acoustic wave, it's the adiabatic bulk modulus divided by the speed of the wave. For an electric circuit, it's a complex number with real part equal to the resistance and imaginary part equal to the reactance. FTP, name this quantity, whose name comes from a Latin word meaning 'entangle,' often denoted in equations as Z.
For an acoustic wave, it's the adiabatic bulk modulus divided by the speed of the wave.
{Impedance}