A generally valid definition of waste energy is proposed. This requires the inclusion of the second law of thermodynamics. The occurrence of internal irreversibilities in all technical processes, as significant loss sources not visible in energy balances, leads to external losses, known as waste energies. The systems considered demonstrate the influence of technology and balance boundaries on the nature and magnitude of losses, as well as the relationship between primary energy balance, anthropogenic processes, and waste energy. Thus, the recovery of waste energy presents itself as the dual aspect of a general energy economic consideration. Starting from such an approach, one speaks of an entropy economy instead of an energy economy following a paradigm shift in the design of optimal technical processes.