"if we imagine the electromagnetic spectrum is like a piano that spans all types of radiation, visible light is essentially a single key about two-thirds of the way down the keyboard. (If you use a logarithmic scale, it is on the order of 2 percent of our measurable spectrum. For a linear scale it is much, much less.) The rest of the notes are grouped into different types of radiation that scientists use to help describe what the radiation does as its frequency increases or decreases."

A very nice discussion this is.