a lovely audio slideshow on the Guardian Science website that attempts to explain the wave equation. It's done by Ian Stewart, who gives it a good dumbing down. But it still sounds complicated to me. And I spent some of my best and brightest years studying this equation in all its realms, from Physics of Music to Optics, Electromagnetism, Geology and Oceanography.
I remember when I changed my major from Industrial Engineering to Physics my grandfather asked me, "What IS Physics?" I didn't have the presence of mind to explain it as well as Ian Stewart. I said something like, "Everything is physics, Granddaddy. Like this..." And picked up a book and dropped it on the sofa. "Gravity is physics." He said, "Oh, I see," and went back to reading those incomprehensible columns of figures in the Wall Street Journal.
I like this wave equation inspired explanation. Physics is the analysis of where things are and when. It's useful for predicting where they will be later if you do different things to them. Things can be ordinary objects like strings, thin membranes, and rocks; or less solid things like water and air; or really esoteric things such as light, radio signals, and atomic scale particles. The same calculus works for all of them.