Harmonic-motion definitions

A periodic vibration, as of a pendulum, in which the motions are symmetrical about a region of equilibrium. Such a vibration may have only one frequency and amplitude or may be a combination of two or more components.

Motion that repeats periodically, as the motion produced by a restoring force proportional to displacement.

A periodic vibration, as of a violin string, in which the motions are symmetrical about a region of equilibrium. Such a vibration may have only one frequency and amplitude or may be a combination of two or more components called harmonics.