Wikipedia quotes “amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communications.” Of course, many will also be familiar with the Tony Hancock radio and TV sketch “The Radio Ham”.
If you are a radio enthusiast and are interested in getting involved with the hobby please take a look at the RSGB’s (Radio Society of Great Britain) pages which very well describe what is needed and what you can do.