Electrical Admittance:

The Admittance (Y) is the inverse of the Impedance (Z). The SI unit of admittance is the Siemens.
Admittance means calculation of how a device or circuit admits or allows Electric Current to flow through it. Admittance is concerned with easy flowing of current through a circuit. An Impedance can be thought of as the "inverse" of admittance.
Y=Inverse of Z=1/Z
where
Y is the admittance, it is measured in siemens Z is the impedance, measured in ohms