AM is amplitude modulation, and FM is frequency modulation. AM was discovered long before FM, and they just never got rid of it. Many talk shows use it to get a wider audience, as AM signals can reach all over the world, where as FM has a roughly 250 mile limit. AM used to be used for everything including music, until they discovered FM signals could carry stereo instead of mono sound, and the quality was much better, because the wavelengths were more concentrated and smaller.
