Entropy is a macroscopic property of a system that is a measure of the microscopic disorder within the system. It is an important part of the second law of thermodynamics. Thermodynamic systems are made up of microscopic objects, e.g. atoms or molecules, which "carry" energy. According to the second law of thermodynamics, the thermodynamic entropy is a measure of the amount of energy which does no work during energy conversions.In applied thermodynamics, as a matter of convention, entropy is measured in units of energy per temperature (SI: joules per kelvin). If thermodynamic systems are described using thermal energy instead of temperature, then entropy is just a number by which the thermal energy in the system is multiplied. The resulting energy is an energy for which no information is available which would be required to convert the energy in technical systems from one form (e.g. electrical) into another form (e.g. mechanical).
In technical applications, machines are basically energy conversion devices. Thus, such devices can only be driven by convertible energy. The same applies to biological organisms. The product of thermal energy (or the equivalents of thermal energy) and entropy is "already converted energy". This is the reason why Rudolf Clausius coined the term "entropy" based on the Greek εντροπία [entropía], from εν- [en-] and (τροπή [tropē] (turn, conversion
