1. The sounds in audio or areas of data that are bad or not wanted. Data corruption may create a noisy transfer if a detection system is used. Some machines can produce annoying noises depending on a sounds amplitude, frequency, severity, duration and persistance.
Electrical hardware often develop interference noise. Such interference takes the form of extraneous signals which might create false information from the corrupted data. Urban sources of background noise include other people's activities, aeroplanes, barking dogs and motor vehicles.
2. Noise can also come from common Language, Usenet, Weblogs and Email lists in the form of spam or false information, etc. When some people talk it can be noisy because of the kind of information they discuss, the manner in which the dialogue is presented and the way the source is percieved.
3. Line Noise - result from electromagnetic waves transferred from active wires that are too close together or from an unsheilded, high-voltage wire. This is a common term in analog systems such as modems and in audio, creating a sharp or dull humming noise.
4. A music genre. 'Noise' music is made by making noise. It can be about anything variating from flowing water to crashing glass, from a motor from a car to a number of wine bottles each a different size and a different # of content. Sometimes hard to define, noise music demands creativity and imagination from both the author as well as the listener. Also see jam session. Not a Bad Thing, like the other 3 entries.