Figure: A simple Wave

The word "waves" makes most (normal) people think about waves crashing on a beach, not electromagnetic radiation. But both kinds of waves have some things in common, such as crests, troughs, wavelength, and frequency.

Credit: Physics 2000, Colorado University at Boulder, http://www.colorado.edu/physics/2000/index.pl.

http://www.colorado.edu/physics/2000/waves_particles/waves.html