1. Any integral multiple of the lowest (or fundamental) frequency of a physical system. For example, the motion of a taut, gently plucked violin string is the superposition of sinusoidal motions with frequencies ω0, ω1 = 2ω0, ω2, 3ω0,. . . Where ω0 is the fundamental frequency and ω1, ω2,. . . Are the harmonics (or overtones), resulting in a harmonious composite sound. 2. A sine or cosine component of the Fourier series representation of an empirical or theoretical function.