The term Radio frequency refers to electromagnetic radiation in the range of frequencies lower than microwaves. Radio waves at these frequencies have been found useful for long-range communications. Among these frequencies, shortwave radio communications operate at frequencies that can be reflected by the ionosphere and therefore can bounce around the earth. Longwave frequencies are used for relatively short range communications such as the most ordinary of the commercial amplitude modulation (AM) radio stations. Their transmissions ordinarily do not get long bounces.