The admittance (Y) is the reciprocal of the impedance (Z). It is a complex quantity resulting from 1/Z.
Like impedance, admittance consists of an effective component, the frequency-independent effective conductance (G), and the imaginary, frequency-dependent component, the reactive conductance (jB). The geometric addition of both components forms the admittance or the apparent conductance.
This quantity is used, among other things, to determine the frequency-dependent conductance of RF components such as antennas, connectors or high-frequency cables, whose apparent conductance is shown in Smith charts.