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.
a Radioafección 
