Zeroth Law of Thermodynamics

* If two thermodynamic systems are in thermal equilibrium with a third, they are also in thermal equilibrium with each other.

This is named zeroth law because it is basic law that is formulated after the three laws are formulated. The above is the actual statement for Zeroth law of Thermodynamics. This can be understood as follows

* When two bodies, of which one is at a higher temperature than the other, are kept in contact, heat energy flows from the one at the higher temperature to the one at lower temperature.