The term energy has an important physical meaning in physics and is an extremely useful concept. A much more abstract
mathematical generalization is defined as follows. Let be a Space with Measure and let
be a real function on the Product Space
See also Dirichlet Energy, Mutual Energy
Iyanaga, S. and Kawada, Y. (Eds.). ``General Potential.'' §335.B in
Encyclopedic Dictionary of Mathematics. Cambridge, MA: MIT Press, p. 1038, 1980.