1. In electronics, a term used most often, for lack of a better way to describe it, the Quality of a circuit, inductor or transmission. 2. Quality factor of an inductor or capacitor. It is the ratio of a component's reactance (energy stored) to its effective series resistance (energy dissipated). For a tuned circuit, a figure of merit used in bandwidth calculations. Q is the ratio of reactive power to resistive power in a tuned circuit.