The meaning of thermal equilibrium
The thermal balance of two objects, or the thermal balance of two thermodynamic systems, simply means:
1. Thermal balance ≡ equal temperature.
2. Thermal balance is only a macroscopic concept of balance, △Q = 0; however, there is still thermal exchange at the microscopic level.
3. Thermal balance is a state quantity, which does not involve the establishment of a process, nor does it exclude the ongoing micro-process.