Electromagnetic radiation, also EM radiation, was a broad term for any type of radiation that exists on a spectrum ranging from long to short wave, in the order of: radio, microwave, infrared, visible light, ultraviolet, x-ray, and gamma ray.
In 2152, Doctor Phlox tried to free Jonathan Archer from a symbiotic lifeform using electromagnetic radiation, but to no avail. (ENT: "Vox Sola")
A mysterious vessel discovered by Enterprise NX-01 originating from the 31st century, was able to, among other things, absorb electromagnetic radiation. (ENT: "Future Tense")
Borg were able to see most of the EM spectrum through their eyepiece. (ENT: "Regeneration")
Pulsars emit various kinds of electromagnetic radiation. (TNG: "Samaritan Snare")
The warp field of a Federation starship like the USS Enterprise-D left behind an electromagnetic signature on Data's internal servo fluid system. (TNG: "Schisms")
Graviton ellipses are known to be attracted to electromagnetic radiation. The USS Voyager once reduced its power in order to lower the EM radiation levels and avoid one such ellipse. (VOY: "One Small Step")