Shot noise is a type of electronic noise which originates from the
discrete nature of electric charge. Shot noise in electronic circuits
consists of random fluctuations in a DC current because current actually
consists of a flow of discrete charges (electrons). With very small
currents, particularly when measuring on short time scales (thus wider
bandwidths), shot noise can be significant. The term also applies to
photon counting in optical devices, where shot noise is associated with
the particle nature of light (photons).