ABSTRACT
The thermodynamic theory consists of defi nitions, laws, and corollaries, based on experimental facts. In this chapter we explain and clarify these concepts.
Defi nitions should be stated in exact terms allowing no room for ambiguity, thus providing a common language for all the users of the subject. One can defi ne any concept, regardless of whether it exists in reality or not. For example, a mermaid may be clearly defi ned as a creature having an upper part of a young woman and a lower part of a mature fi sh; yet, the very fact that it can be well defi ned does not guarantee its actual existence.
