What does E=MC2 stand for?

You always hear about how Albert Einstein failed math in school because he was a genius and it was too boring for him. Then there are those of us that failed math because we simply suck at it.

Of course, turns out that was a myth to begin with, considering Einstein had mastered calculus by the time he was a teenager. He would go on to develop equations and theories that have become fundamental to our modern understanding of the universe.

I mean, I could go ahead and list some of his more complicated and very long equations here, but I think I already mentioned the not-good-at-math thing. So instead, let's go with everyone's favorite, and one that's short enough for me to memorize.

You heard it in school at least once — what does E=MC2 stand for?