  A single term of the thermodynamic theory such as ‘entropy’ will be associated with a wide variety of concepts defined in the newer account. There is, for example, Boltzmann entropy which is the property of a single system defined in terms of the spatial and momentum distribution of its molecules. On the other hand there are the Gibbs'entropies, definable out of the probability distribution over some Gibbsian ensemble of systems. Adding even more complications there is, for example, Gibbs' fine grained entropy which is defined by the ensemble probability alone and is very useful in characterizing equilibrium states and Gibbs' coarse grained entropy whose definition requires some partitioning of the phase space into finite cells as well as the original probability distribution and which is a useful concept in characterizing approach to equilibrium from the ensemble perspective. In addition to these notions which are measure theoretic in nature, there are topological notions which can play the role of a kind of entropy as well.