Perhaps the most famous formula in existence, Einstein's Mass-Energy Equivalence Formula changed the way we look at the world. In physics — in particular, special and general relativity — mass-energy equivalence is the concept that the mass of a body is a measure of its energy content.

E = Energy
m = Mass
c = The Speed of Light in a Vacuum

More info can be found here: http://en.wikipedia.org/wiki/Mass-energy_equivalence