Zeroth law of Thermodynamics

The zeroth law of thermodynamics states that if two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.

It deals with thermal equilibrium and basis for temperature measurement. It also gives the concept of isotherm.

Zeroth Law

The above diagram says that A is in thermal equilibrium with B & B is in thermal equilibrium with C then A and C are also in thermal equilibrium.