Mass-energy

An important year in scientific history is 1905, when Einstein changed the face of physics with his theories of special relativity, mass-energy equivalence and the photoelectric effect.

Source: tatoeba (1516427)

Scientists theorize that stars, planets and the molecules they contain represent less than five percent of the mass-energy content of the universe. The rest is dark energy and dark matter, which cannot be directly detected.

Source: tatoeba (8764013)

Whereas in classical physics mass and energy are distinct concepts, on relativistic scales, they become indistinguishable and are replaced by mass-energy.

Source: wiktionary

In higher-energy physics, mass and energy eventually become meaningless as individual concepts; a particle's so-called "mass" is actually mass-energy and is often given equivalently in units of either mass (GeV/c²) or energy (GeV).

Source: wiktionary