Ham radio (so called because its operators were originally derided as being 'hammy' in the 19th century, when the technology first emerged) is a term that applies to any form ofamateur radio broadcasting.
There are designated radio frequency spectra available solely for public use. Uses range from recreation to communication and the non-commercial exchange of ideas. 'Hams' take advantage of these frequencies in order to transmit any number of things
Strictly speaking, there should not be any money involved in amateur radio (hence the term 'amateur'). Although the majority of Ham radio practitioners are actually extremely knowledgeable about radio technology (don't let the 'ham' part fool you), they are not considered professionals because they do not profit from their endeavours. Conversely, commercial broadcasting involves (a lot of) money: royalties are paid, producers and performers are paid and the whole thing is ultimately a commercial exercise.
Hams use a large amount of frequency bands from all across the radio spectrum, but the majority of frequencies are to be found just above the AM band.
A lot of hams, however, use VHF FM, operating hand-held transceivers that send on one frequency and receive on another. Local radio clubs set up FM Repeaters (which borrow space from other broadcast devices such as towers and, in doing so, amplify the radio signal's strength hundreds of times over), so that hams can communicate with each other wirelessly over a distance of hundreds of miles.
As an example of what hams get up to, here's an excerpt from Gary Brown, of How Stuff Works.com
"Although a ham radio does broadcast in all directions, hams generally do not use their radios in a broadcast kind of way as a disk jockey would at a radio station. In normal AM or FM radio, one disk jockey transmits and thousands of people listen. Hams, on the other hand, conduct two-way conversations, often with another ham or with a group of hams in an informal roundtable. The roundtable of hams may be in the same town, county, state, country or continent or may consist of a mix of countries, depending on the frequency and the time of the day. Hams also participate in networks, often called nets, at predetermined times and frequencies to exchange third-party messages. In the case of disasters, hams exchange health and welfare information with other hams".
To become a ham, I recommend that you join a club. You'll need an amateur radio license, of course, but this won't break the bank, I'm sure.
I hope that helps, Melissa.