From AMS Glossary
(Also energy transformation, energy transfer.) A process in which energy changes from one form to another.
Energy is conserved for a system that does not interact with its surroundings, and the total energy of such a system may often be expressed as the sum of energies of different kinds:
Thus if E1 decreases in any process, E2, etc., must increase correspondingly for E to remain constant, and we may say that energy of type 1 has been converted into energies of type 2, 3, etc.