This is a simple question by a simple reader. What are waves made of. We seem to know that molecules are made of atoms and atoms are made of sub-atomic particles and there is speculation that sub-atomic particles are made of waves (in very simplistic terms). So, I'm wondering what makes a wave a wave. There must be a dense to less-dense ratio that helps define a wave. What makes up the density and what offers the medium that is less dense so that the wave is able to vibrate at various frequencies? If this question belongs somewhere else, feel free to put it there, thank you!