resonance frequency

(physics) A frequency at which some measure of the response of a physical system to an external periodic driving force is a maximum; three types are defined, namely, phase resonance, amplitude resonance, and natural resonance, but they are nearly equal when dissipative effects are small. Also known as resonant frequency.
(quantum mechanics) A characteristic frequency, satisfying the Bohr frequency condition, at which a quantum-mechanical system absorbs radiation.