In electronics,
noise is a random fluctuation in an electrical signal, a characteristic of all
electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects.
Thermal noise is unavoidable at non-zero temperature (see
fluctuation-dissipation theorem), while other types depend mostly on device type (such as
shot noise, which needs steep potential barrier) or manufacturing quality and
semiconductor defects, such as conductance fluctuations, including
1/f noise.