Quality Factor: The quality factor basically represents a figure of merit of a component (practical inductor or capacitor) or a complete circuit. It is a dimensionless number and defined as:

In series circuit it is defined as voltage magnification in the circuit at resonance

**OR **

It is also defined as the ratio of the reactive power of either the inductor or the capacitor to the average power of the resistor.

**OR **

In parallel circuit it is defined as equal to the current magnification in the circuit at resonance

**OR **

The quality factor or Q-factor of parallel circuit is defined as the ratio of the current circulating between two branches of the circuit to the current taken by the parallel circuit from the source.