A type of noise signal. Mathematically, white noise is described as a signal in which all possible instantaneous values of the signal are equally likely at any given time. In audio terms, white noise is biased towards the frequencies at the top end of the spectrum; its power increases at a rate of 3 dB/octave in the direction of the higher frequencies. Unfiltered white noise is usually described as "hissy". White noise is often used as a means to synthesize drum, percussion, and wind-noise sounds.
White noise has the virtue that it is uniformly random, which is to say that at any given moment, the output voltage may be any value between the minimum and maximum voltage, and all values are equally likely. For this reason, white noise is often used as a random-control-voltage generator by inputting it into a sample and hold circuit. With this, every time the sample and hold is clocked, it produces a random voltage; feeding this to a VCO produces the ever-popular "random notes" effect. Other uses are certainly possible; for instance, the voltage might be fed to a comparator circuit to clock a sequencer at random intervals.