Electromagnetic radiation, or “EM” radiation, refers to the radiant energy released by certain electromagnetic processes. Electromagnetic radiation consists of electromagnetic waves, which are produced whenever charged particles are accelerated; these waves can interact with any charged particles. Nearly any powerful electromagnetic device, such as a speaker cabinet or computer monitor produces some degree of EM radiation.
EM radiation is an issue for musicians who play electric instruments because those electromagnetic waves can interact and interfere with electromagnetic pickups. This EM radiation interference usually manifests itself in an ugly buzzing noise — that’s the sound of the electromagnetic radiation interacting with the charged particles of the magnets in your pickups. Electromagnetic shielding can help protect pickups from electromagnetic radiation, but the best solution is to turn or take a few steps away to a location in which there isn’t any EM radiation interfering with your gear.