FM stands for Frequency Modulation. Here, the frequency of the carrier wave is varied according to the audio signal, while amplitude remains (mostly) constant. It provides higher sound quality, better resistance to many kinds of interference, and stereo sound. But FM signals generally don’t travel as far as AM signals, especially through obstacles.
Analog radios (like traditional AM/FM) modulate a continuous signal (amplitude or frequency) to carry audio.
Digital radios convert the audio signal into digital data (binary), compress it, then transmit. The receiver decodes the digital signal into audio. Digital radio can offer better quality, more stations in the same spectrum, metadata (like song/artist info), etc. Examples include DAB, HD Radio, DRM
AM radio typically operates between ~535 to 1705 kHz (kilohertz) for medium wave in many countries. FM radio typically operates between ~88 to 108 MHz (megahertz).
