Step 1: Statement of Zeroth Law
If two bodies are each in thermal equilibrium with a third body, they are in thermal equilibrium with each other. Step 2: Interpretation
This law introduces the concept of temperature as the physical quantity that determines thermal equilibrium. Step 3: Meaning of thermal equilibrium
Two bodies in thermal equilibrium have the same temperature and no net heat flow between them. Step 4: Conclusion
Therefore, temperature is the common quantity in thermal equilibrium.