White Noise

“In signal processing, white noise is a random signal having equal intensity at different frequencies, giving it a constant power spectral density. White Noise is a discrete signal, whose samples are regarded as a sequence of serially uncorrelated random variables with zero meaning and finite variance; a single realization of white noise is a random shock.”
 
“White noise is often used in engineering and natural sciences to illustrate faults in an otherwise ideal model. Noise and other interferences are subjectively perceived as less loud when superimposed with white noise.”

(Wikipedia)