AM (amplitude modulation) was the early mode used by hams for voice transmission. In AM the signal is a carrier (like CW) that has upper and lower sidebands that are modulated by varying the amplitude (strength) of the signal. Most shortwave broadcast stations use this method. If you tune to the BBC or some such station using either USB or LSB on your receiver you can hear the carrier as a continuous tone as you move slightly away from the center of the signal. If you listen around the upper end of the 80 meter band you may find some hams using this mode. However AM takes twice the bandwidth of SSB and so is not widely used in Amateur radio.