Reply to classmate forum, When two systems are in thermal equilibrium, they are at the same temperature, and there is no net flow of thermal energy between them. This means that if the systems are in thermal contact, or can exchange heat, no heat will flow because their temperatures are equal. This concept is foundational in thermodynamics and is described by the Zeroth Law of Thermodynamics, which states that if two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other