AM (520 to 1610/1710 KHz) is "Amplitude-Modulation",
and FM (87.5 to 108 MHz) is "Frequency-Modulation".
We can generally hear frequencies from 20 to 20,000 Hz.
Both AM & FM utilize a carrier-wave
(think of it as a high-pitched whistle).
AM transmits information by modulating the carrier-wave's-amplitude/volume,
whereas FM transmits information by modulating the carrier-wave's-frequency/tone.
FM is less-prone to common-interference.