The Clue The "m" in Einstein's E = mc2
The Answer MASS
In Einstein's famous equation, E = mc², the "m" stands for mass. This equation shows the relationship between energy (E) and mass (m) with the speed of light (c) as a constant. Mass is a measure of how much matter an object contains. So, the answer "mass" fits perfectly as it directly represents the "m" in the equation.