When most people think of waves they think of the waves at the beach. But there are many different types such as sound waves versus microwaves. All together there are two main types, electromagnetic and mechanical. Radio waves would fall under electromagnetic since no medium is required. As you listen to the radio the channel you choose is determined by the frequency which is the amount of waves per second or 1/P. Compared to other electromagnetic waves, radio waves have a smaller frequency but a larger wave length. Wave lengths can be determined by measuring a wave from crest to crest which is usually done in meters. And since you dont need a medium for the wave to travel you can have a satelite in space send the signals all over.