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Shortwave radio refers to the upper MF (medium frequency) and all of the HF (high frequency) portion of the radio spectrum, between 1,800–30,000 kHz.[1] Shortwave radio received its name because the wavelengths in this band are shorter than 200 m (1500 kHz) which marked the original upper limit of the medium frequency band first used for radio communications. The broadcast medium wave band now extends above the 200 m/1500 kHz limit, and the amateur radio 1.8 MHz – 2.0 MHz band (known as the "top band") is the lowest-frequency band considered to be 'shortwave'.
Initially thought to be useless, shortwave radio now has many applications where the behaviour of radio waves in the Earth's atmosphere make long-range communication possible. Shortwave radio is used for broadcasting of voice and music, and long-distance communication to ships and aircraft, or to remote areas out of reach of wired communication or other radio services. Amateur radio on these frequencies can provide hobby, educational and emergency communication.

http://en.wikipedia.org/wiki/Shortwave_radio

is any electromagnetic wave at a radio frequency...