Radio is tough to understand intuitively. There’s plenty of physics to describe its behavior, but it can’t be seen, smelt, felt or heard without special equipment. Radio waves travel without a medium, so the common terminology of “airwaves” is quite misleading. There’s no need for air. Defining it as “wireless” is not helpful. That doesn’t tell us what it is, just what it’s not. Radio is gerbilless too but so what?
In an effort to better describe radio phenomena to my class, I came across several great posters that are freely available as PDF files. One from Unihedron depicts the full electromagnetic spectrum. Another from the NTIA shows the full frequency allocation for radio in the United States. Finally there’s a politically motivated poster from the New America Foundation that shows the financial value and politics of radio spectrum allocation (back).
A printed version of each poster is available from that publisher for a nominal fee. I strongly recommend checking them out.