Abstract: Entropy was defined as dS=cd(E-E_(AV)) and the variation of entropy was consequently considered as a measure of variation of unavailable energy by G. N. Hotsopoulos and J. H. Keenan. But there is stilt room for improvement. Introducing a concept of the so-called permanent disorder energy E_(TO), the authors define entropy as dS=cd E_(To) and consider the variation of entropy as a measure of variation of permanent disorder energy. Thus the definition and the macroscopic interpretation of entropy given by Hotsopoulos and Keenan is improved in this paper. Once c=1/To is selected, the new macroscopic definition of entropy is consistent with the traditional expression.