1. The emission and propagation of radiation associated with a periodically varying electric and magnetic field traveling at the speed of light, including gamma gray X-rays, and ultraviolet, light, infrared, and radio waves.
2. A reconnaissance activity for the purpose of locating and identifying potentially hostile transmitters of electromagnetic radiation, including radar, communication, missile-guidance, and navigation-aid equipment.

Identification generally includes determination of frequency, type of modulation, pulse data, antenna characteristics, and bearing to the transmitter.