It is the study of electronics, radio waves, and most of all, it's fun.
Within amateur radio, one can pursue fascinating topics such as [antenna theory]?, [satellite communication]?, DX communication over thousands of miles using the ionosphere to refract radio waves, and low-power or QRP operation.
See also Morse code, electromagnetism, and Electromagnetic radiation.
For more information, please see http://www.arrl.org
With the advent of the internet (offering email, music, broadcast audio, video, voice over IP VoIP) the popularity of ham radio is diminishing in advanced countries. In 2001, the BBC reduced or eliminated its shortwave broadcasts to North America.