Probably from wikipedia:
White noise is a random signal (or process) with a flat power spectral density. In other words, the signal contains equal power within a fixed bandwidth at any center frequency. White noise draws its name from white light in which the power spectral density of the light is distributed over the visible band in such a way that the eye’s three color receptors (cones) are approximately equally stimulated.
An infinite-bandwidth, white noise signal is purely a theoretical construction. By having power at all frequencies, the total power of such a signal is infinite and therefore impossible to generate. In practice, however, a signal can be “white” with a flat spectrum over a defined frequency band.
Noise in analog video and television is perceived as a random dot pattern which is superimposed on the picture as a result of electronic noise and radiated electromagnetic noise picked up by the receiver’s antenna—it is the “snow” which is seen with poor analog television reception or on VHS tapes.
When there is no transmission, which is to say no signal, the noise or “snow” is due mostly to thermal noise from the device itself, stray electromagnetic fields from other household electric devices, and other electromagnetic signals, all of which is interpreted as luminance signal.
UK viewers used to see “snow” on black after sign-off, instead of “bugs” on white, a purely technical artifact due to old 405-line British receivers using positive rather than the negative video modulation used in Canada, the U.S., and (currently) the UK as well.
Since one impression of the “snow” is of fast-flickering black bugs on a cool white background, in Sweden, Denmark and Hungary the phenomenon is often called Myrornas krig in Swedish, Myrekrig in Danish and “Hangyák háborúja” in Hungarian, which translate to “War of the Ants” and “Ant war”.
Radio noise in radio reception is the superposition of white noise (also called “static”) and other disturbing influences on the signal, caused either by thermal noise and other electronic noise from receiver input circuits or by interference from radiated electromagnetic noise picked up by the receiver’s antenna. If no noise was picked up with radio signals, even weak transmissions could be received at virtually any distance by making a radio receiver that was sensitive enough. In practice this doesn’t work, and a point is reached where the only way to extend the range of a transmission is to increase the transmitter power.
Thermal noise can be made lower by cooling the circuits, but this is only usually worthwhile on radio telescopes. In other applications the limiting noise source depends on the frequency range in use. At low freqencies (longwave or mediumwave) and at high frequencies (shortwave), interference caused by lightning or by nearby electrical impulses in electrical switches, motors, vehicle ignition circuits, computers, and other man-made sources tends to swamp transmissions with thermal noise. These noises are often referred to as static. Atmospheric noise is radio noise caused by natural atmospheric processes, primarily lightning discharges in thunderstorms. At very high frequency and ultra high frequency these sources can still be important, but at a much lower level, such that thermal noise is usually the limiting factor. Cosmic background noise is experienced at frequencies above about 15 MHz when highly directional antennas are pointed toward the sun or to certain other regions of the sky such as the center of the Milky Way Galaxy.
Electromagnetic noise can interfere with electronic equipment in general, causing malfunction, and in recent years standards have been laid down for the levels of electromagnetic radiation that electronic equipment is permitted to radiate. These standards are aimed at ensuring what is referred to as electromagnetic compatibility, or EMC.
The title ‘White Noise’ refers to the phenomenon known as Electronic Voice Phenomena (EVP). People believe that you can hear voices of the dead in the white noise of a detuned radio and even see faces from the white noise on the television set. Michael Keaton stars in this thriller as Jonathan Rivers, a man who had just lost his wife in a freak accident. Raymond Price (Ian McNeice) meets with Jonathan and tells him that his wife Anna has contacted him from the other side. Jonathan doesn’t believe him until he hears Anna’s voice on his radio. Jonathan wants to talk to his wife, and he gets all the equipment. There is only one thing that Jonathan doesn’t know, there are also bad people on the other side. Douglas Young (the-movie-guy)