What is Noise ?

Undesired electical which are introduced with a message signal during the transmission,our processing of the latter. are called Noise.  Noise, is unwanted signal that corrupts desired message signal. ln general, noise may be predictable or unpredictable (random) in nature. The predictable noise can be estimated, and eliminated, by proper engineering design.  Some  examples of such noise are:power supply hum, oscillation in feedback amplifers, ignition radiation pick-up, radiation pickup generated by  electrical appliance,  and fluorescent lighting. The predictable noise,  generally is man-made and can be  reduced or eliminated.
Unpredictable noise varies randomly with time and, as such, we have no control over this noise. Identifications of the message signal at the receiver depends upon the amount of noise accompanied by the message during the process of communication.  In the absence of noise, identification of the message signal receiver is perfect.The amount of noise present in the received signal decides the minimum power level of the desired message signal at the transmitter.  The term noise is normally used to refer the unpredictable or random noise.