Thermal equilibrium refers to a state in which two or more objects or systems are at the same temperature and there is no net transfer of heat between them when they are in contact.

In thermal equilibrium:

1. There is no net flow of heat between the objects or systems.
2. The temperatures of the objects or systems are equal.
3. The thermal energies of the objects or systems are also equal.

When two objects or systems are brought into thermal contact with each other but they are at different temperatures, heat will flow from the hotter object to the cooler one until they reach thermal equilibrium. This process continues until the temperatures of the objects become equal.

Thermal equilibrium is a fundamental concept in thermodynamics and plays a crucial role in understanding heat transfer, temperature dynamics, and the behavior of systems in contact with each other.