What is admittance?

Admittance, represented by the symbol Y, is a measure of how easily a circuit or device will allow AC current to flow. Mathematically, it is defined as the reciprocal (or inverse) of impedance (Z). Thus, Y = 1/Z. Just as impedance is a complex number made up of resistance and reactance, admittance is a complex number made up of conductance and susceptance. It is measured in Siemens (formerly called mhos). Other options are incorrect definitions for different concepts. For example, the inverse of reactance alone is known as susceptance, not admittance.