You are probably talking about the Theory of Everything. Originally this equation was a very long, complicated equation that attempts to explain all of the laws of physics, particles of the universe, their characteristics, and their relation to one another. The easiest and most compact form of this equation is the Lagrangian form which tries to explain the maximum amount of energy the system can contain.
The first section of the equation is specific to the gluon particle. The second section is the explanation of the boson interaction. The third section is devoted to elementary matter particles, the fourth is based on how particles deal with the Higgs ghost, and the fifth section includes Faddeev-Popov ghosts which negates redundancies found in weak force interactions
I think you are refering to the equation postulated by Stephen Hawking. The equation is a theory of how the universe may be connected but it is a bit of a misnomer in that it cannot explain everything, rather it explains how everything is connected.
The theory links together all the physical aspects of the universe to explain how the universe was created and what will happen as the universe continues to expand.