Amplitude Modulation (AM) is a type of modulation. An AM signal is produced by varying the strength of a radio signal proportional to the information bearing signal.
Amplitude modulation was the first type of modulation used for the transmission of information from one point to another. Nowadays, AM is not much used anymore.
AM is used for radio broadcasting in three frequency bands: medium frequency (also known as medium wave); low frequency (also known as long wave) and high frequency (also known as short wave). The term AM is often used to refer to the medium frequency band.