The zeroth law of thermodynamics: If bodies A and B are each in thermal equilibrium with a third body T,then they are in thermal equilibrium with each other. Or in plain word,we could use a certain property to describe the state of body in thermal equilibrium The zeroth law of thermodynamics: If bodies A and B are each in thermal equilibrium with a third body T, then they are in thermal equilibrium with each other. Or in plain word, we could use a certain property to describe the state of body in thermal equilibrium