rest energy(n = noun.phenomenon) - the energy equivalent to the mass of a particle at rest in an inertial frame of reference; equal to the rest mass times the square of the speed of light;
is a kind of energy, free energy

activation energy, alternative energy, at rest, atomic energy, atomic energy commission, bed rest, binding energy, chemical energy, chin rest, conservation of energy, day of rest, department of energy, department of energy intelligence, elastic energy, elastic potential energy, electrical energy, energy, energy department, energy level, energy of activation, energy secretary, energy state, energy unit, eternal rest, geothermal energy, gun rest, half rest, heat energy, high energy physics, international atomic energy agency, kinetic energy, law of conservation of energy, lay to rest, libidinal energy, luminous energy, mass energy, mechanical energy, mental energy, nuclear energy, potential energy, psychic energy, quarter rest, radiant energy, rest, rest area, rest assured, rest cure, rest day, rest home, rest house, rest mass, rest on, rest period, rest room, rest stop, secretary of energy, separation energy, solar energy, waste of energy, whole rest, wind energy facility