Amateur radio, also called Ham radio,
is a hobby and a public service enjoyed by about 6 million people throughout the world.
An amateur radio operator, also known as a ham or radio amateur, uses advanced radio equipment to communicate with
other radio amateurs for public service, recreation and self-training.
(Wikipedia)
This is the official definition of Amateur radio by
ITU:
«A radiocommunication service for the purpose of self-training, intercommunication and technical investigations carried
out by amateurs, that is, by duly authorized persons interested in radio technique solely with a personal aim and
without pecuniary interest».
To use amateur radio bands you need an authorization that you can obtain after an
examination.
In Spain this is the procedure to follow.
Amateur Radio 
