Entropy is a property of thermodynamical systems. The term entropy was introduced by Rudolf Clausius who named it from the Greek word τρoπή, "transformation". He considered transfers of energy as heat and work between bodies of matter, taking temperature into account. Bodies of radiation are also covered by the same kind of reasoning. More recently, it has been recognized that the quantity 'entropy' can be derived by considering the actually possible thermodynamic processes simply from the point of view of their irreversibility, not relying on temperature for the reasoning.