Any quantity or body is in a state of oscillation when its value or motion is continually changing so that it passes through maximum and minimum values or positions. When a system, body or quantity is set in period motion or vibration, it is said to be in oscillation.
A swinging pendulum, a vibrating string, and a bobbing buoy are all examples of oscillation and simple harmonic motion. However, random noise is also an oscillation since it passes through maximum and minimum values. Oscillations whose frequency lies within the audible range are heard as sound. (Source: Barry Truax - Handbook for Acoustic Ecology CD-ROM Edition. Cambridge Street Publishing, 1999 - CSR-CDR 9901)
See also:Frequency, Harmonic, Inharmonic, Noise