Interference with a desired signal caused by the coupling of an undesired signal due to electromagnetic radiation.The source of the electromagnetic interference may be natural, such as solar radiation, or artificial, such as a generator, compressor, fluorescent light, or electrified copper circuit. The radiation may be in many forms, including radio waves, light waves, and gamma rays. Unshielded twisted pair (UTP) and radio circuits are particularly susceptible to EMI. EMI that is in the radio frequency range is known as radio frequency interference (RFI). See also noise and RFI.