AM stands for Amplitude Modulation, a method of transmitting information (such as an audio signal) by altering the amplitude (the "volume" or "strength") of a high-frequency carrier wave.

Imagine you are using a flashlight to send a signal in Morse code. The light from the flashlight is the carrier wave.

To send the information, you don't change the color of the light (frequency), but rather its intensity: you make it stronger or weaker to form the dots and dashes. Amplitude Modulation does exactly that: A high-frequency carrier wave (the "light" of the radio) is taken. The audio signal that you want to transmit is used to modulate, that is, to vary the amplitude of this carrier wave. Volume peaks in the audio correspond to amplitude peaks in the carrier wave. The radio receiver (the demodulator) detects these amplitude variations and "translates" them back into the original audio signal. AM vs. FM

This method contrasts with FM (Frequency Modulation), where the amplitude of the carrier wave remains constant, but its frequency varies to carry the audio information. AM radio is more susceptible to electrical noise interference, as many noises are also amplitude variations, while FM radio tends to have a cleaner sound with greater fidelity.