Technically,
any energy that moves through something is called radiation. Light from the sun
traveling through space, radio waves from your local station traveling through
the air, and heat traveling from a hot iron to your hand are all forms of
radiation. It’s handy to sort the different forms of radiation based on how
much energy each one contains. If you were to take all of the different kinds
of radiation in the universe and arrange them from lowest energy to highest
energy, you would have what scientists call The Electromagnetic Spectrum or EM
Spectrum, for short.