What are Electromagnetic Waves as noted in the nonfiction book, The New Way Things Work?

Known in general as rays, electromagnetic waves span vibrating electric fields. They are visible to us as light rays, but the visible rays occupy only the central part of the spectrum. Longer electromagnetic waves include radio, TV, microwave and infrared waves. Shorter rays include gamma and x-rays. Electrons must be accelerated to create any of the waves longer than the very short gamma rays.