Electromagnetic describes something that has to do with both electricity and magnetism at once, or that has both kinds of quality. Light, radio waves, X-rays, and microwaves are all electromagnetic waves: they are not “just electric” or “just magnetic.” You also hear electromagnetic field around power lines, phones, and motors. It is a science and technical adjective; news stories use it when they talk about radiation or wireless signals. Though actually, people sometimes say electromagnetic when they only mean “electric” or only mean “a magnet,” which is looser than a physics teacher would like. The careful use keeps both sides in the word.