Noise

(1) a sound which contains all of the frequencies in the audible range.

(2) An unwanted sound which is not related to the wanted sound; if it is, it is called distortion. Noise is comprised of all audio frequencies at constantly varying amplitudes, therefore, it has no definable pitch or timbre. 

See white noise, pink noise, residual noise, ambient noise, quantization noise, modulation noise, NC-Curve, noise floor.