In physics and chemistry, the term "E" is often used as an abbreviation for energy in equations. Since energy can take different forms and has various relationships with matter, motion, light and other scientific concepts, "E" appears in many different equations.
One common example is the equation for the kinetic energy of a moving object: E = 1/2mv^2, in which "E" is the kinetic energy, "m" is the mass of the object and "v" is its velocity.
Another example is an equation for which Albert Einstein received great acclaim: E = mc^2, which describes the equivalence of energy and mass. This equation is used to calculate the amount of energy in a nuclear reaction, where "m" is the difference in mass before and after the reaction and "c" is the speed of light.