Light through a vacuum travels at 300,000,000 meters per second. Light also behaves like a wave, and, thus, every photon has a wavelength. It is these different wavelengths of light that appear as color to our eyes. Different colors of light and indeed, all the different types of electromagnetic radiation have different wavelengths. For the purposes of our course, it's not important that we remember the electrical and magnetic part, but it is important that we recognize the types of electromagnetic radiation.
Electromagnetic radiation is divided into different types according to an electromagnetic spectrum.
The part of the electromagnetic spectrum that we see is known as visible light. Cosmic rays and gamma rays occupy the short-wavelength end of the electromagnetic spectrum. Ultraviolet light is mostly filtered out by ozone in our atmosphere but as ozone concentrations in our atmosphere have fallen in recent years, more uv-radiation is reaching our planet's surface. UV-radiation is known to damage DNA, causing mutations and possibly cancer, so you can see why there is great concern for decreases in atmospheric ozone. The take-home message here is that the electromagnetic spectrum is characterized by radiation of different wavelengths.