Definition of shortwaves:
(n) :
(physics) An electromagnetic wave having a wavelength between approximately 10 and 100 meters, corresponding to frequencies between 3 and 30 MHz.
(adj) :
(of radio waves) Having a wavelength of approximately 10 to 100 meters.
(adj) :
(of radio equipment) Capable of transmitting or receiving signals at such a wavelength.
(n) :
(colloquial, usually in the plural) Any frequency in this range, especially when used in broadcasting.
(n) :
(meteorology) Downward radiation entering the earth's atmosphere that is in the shortwave frequency range.