Two thermodynamic systems are in thermal contact when their boundary permits heat transfer. They need not already be in thermal equilibrium: contact between unequal temperatures is precisely how equilibration can begin. Contact specifies an allowed exchange; equilibrium specifies its balance.
Thermal contact refers to the interaction at the interface between two materials that are in thermal contact with each other. This contact affects the transfer of heat between the materials. When two surfaces are brought together, they do not have perfect contact due to microscopic irregularities, leading to gaps and variations in contact area. These irregularities influence thermal conductivity and the overall thermal resistance at the interface.
New to topics? Read the docs here!