We wish to propose, to the scientific community of soil science, the definition of the term OWN ENTROPY (Sp) as a measure of the degree of internal homogeneity that has any open system. The application of thermodynamic classic laws make it possible to determine the available free energy for a system derived from a function of their evolutionary cycle, understood from their origin until it reaches the condition of stable state. In this work we understand by Open System the Pedogeomorphological System (PGS) defined as that component of the Ecological System conformed by soil, regolite, sediment, rock, and hydrological subsystems, in interrelation with their environment formed by the atmosphere, the biosphere and other PGS. The interface solid-liquid-gas-biota that characterizes the PGS, through which takes place the matter exchange, energy and information inside of and among the ecosystems, can be as small as the surface of a pedon or polipedon or as big as the surface of the whole planet. The theoretical basis that supports this proposal is based on the three classic principles of thermodynamics, that is the Energy Conservation, the Entropy and the Free Energy necessary for the evolution of the PGS. Indeed, it is considered that the PGS is an entity that has an own internal organization, reason why it should have an internal energy of formation, as well as an OWN ENTROPY that adds to the energy and entropy of formation to the individual components of the PGS. A theoretical analysis was carried out around the stated variables that are implicit in the second and third thermodynamic laws. With its base in a wide revision and discussion of the state of the art that served as referential mark for the synthesis of this work, we point out that: 1) the Multiple Homogeneity Index (MHI) it is a equivalent parameter of the OWN ENTROPY of the PGS, MHI = Sp; 2) the MHI was defined as the accumulated product of the own values biggest or similar to one ((&lambdaj &ge 1,0000), where &lambdaj are the characteristic roots or own values (Eigenvalues) determined through the Principal Components Analysis (PCA); 3) Such an index allows to establish comparisons with the purpose of studying the structure, dynamics, evolution, stability and space variability of suchs attributes inside the system and from this with relationship to other systems, including the entirety surrounding environment. To calculate the MHI its multiplies the first own value by the second, the obtained product its multiplies by the third and so forth until using all the own values bigger or similar to one. Algebraically it is represented by means of the following equality: m MHI = &Pi&lambdaj j=1 where &Pi =mean accumulated product of...";&lambdaj is the characteristic value of the j principal component whose magnitude is &ge 1,0000 and 4) The MHI has been validated in diverse studies like: Homogeneity analysis of cartographic units of soils and landscape; b. - Definition of soils types; c. - Pedogeomorphological analysis in sequences of soils and landscapes; d. - Studies of mesoclimate homogeneity of Venezuela life zones. With base on the state of art previously summarized we concludes that under similar formation conditions, determined by the same number and type of pedogeomorphological characteristic and under similar exchange flow of matter, energy and information with the surrounding environment, two PGS could exhibit a degree of internal homogeneity different between them which can be determined starting from the MHI. In consequence, the PGS that possesses the largest value in the MHI will be most likely to reach a stable condition characterized by a maximum OWN ENTROPY and a minimum variation of its Free Energy in comparison with that one whose MHI is of a smaller value. Key words: Entropy, Free Energy, Multiple Homogeneity Index, Ecosystem, Soil and Landscape.