ThermEvery system has certain characteristics by which its physical conditions may be described which depends upon its state but not upon how the state is reached for example volume, temperature, pressure, etc. Such characteristics are called Properties of the System. These are all macroscopic in nature. When all the properties of a system have definite values the system is said to exist at a definite state. Properties are the coordinates to describe the state of a system. They are state variables.
There are some other properties of a system which can neither be observed or obtained by mathematical operations of other properties but only can be defined by means of laws of thermodynamics. Two such properties are: