Radio is a part of the electromagnetic spectrum - minute variations in electricity and magnetism that, like ripples on a pool, spread out in waves at the speed of light to give us light itself, x-rays and other rays, and radio. 
 

Suggested theoretically by James Clerk Maxwell in 1873, identified by Heinrich Hertz in 1887 and given practical value by Guglielmo Marconi in 1895, the radio part of the electromagnetic spectrum ranges from a frequency of about three thousand cycles per second to thirty billion cycles per second. Marconi's early experiments were in the lower frequencies.  

Today every part of the spectrum is used nationally and internationally in applications including terrestrial and satellite television and sound broadcasting, mobile telephones, radar, amateur and Citizens' Band radio, satellite navigation, air traffic control, radio-astronomy... the list is endless. Give radio its old and more descriptive name - wireless - and consider that in most communication where wire (or optical cables these days) is not involved, wireless is. The instant news report from around the world, the cockpit pictures from the Grand Prix car, the next-generation refrigerator telling the cooker the temperature for the casserole - they all rely on wireless technology.

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