It is an important approach to solve energy problem by improving performance of heat transfer process. The macro physical meaning of new physical quantity for heat transfer process optimization “entransy” is analyzed by comparing it with interrelated concepts in mechanics. From three aspects: the connection of entransy and the external heat transfer ability, efficiency of heat transfer process defined by entransy, and the relation of heat transfer driving force with entransy, the macro physical meaning of entransy is derived, which is the potential energy of heat in the temperature field. Moreover, the application of entransy theory in engineering is introduced through entransy theory optimization in convective heat transfer.