Thermodynamics describes the general theory of energy and substance conversion. The fundamentals of thermodynamics deal with the behaviour of systems during temperature changes.
The thermodynamic state variables describe the measurable properties of a system. Any thermal equilibrium state can be unambiguously described by means of state variables.
Heat transfer takes place in two fundamentally different ways. A distinction is made thereby between material-bound (convection and heat conduction) and non-material bound (radiation).
A gaseous, liquid or solid state is called phase. Phase transition is the change from one phase to another.