# Ambiguity in the Definition of Resonance Frequency

we know that in a series LC circuit the resonance frequency is defined as that frequency in which the total impedance offered by the circuit is zero.

We also know that in a parallel LC circuit the resonance frequency is defined as that frequency in which the total admittance offered by the circuit is zero.

I have seen several times analyzes of much more complex circuits (composed of several series and more parallel elements of L and C) in which the resonance frequency was defined as that frequency in which the total admittance was infinite, for example.

My question is: what is the general definition of "resonance condition"? With what criterion do we define the resonance condition for a given circuit?