Thermal is an adjective derived from thermodynamics and heat transfer science. In engineering and physics, thermal pertains to heat, temperature, and the mechanisms by which thermal energy is generated, stored, transferred, or converted. Heat is defined as energy in transit across a system boundary due solely to a temperature difference. Therefore, when a quantity, property, or process is described as thermal, it directly relates to temperature effects or heat transfer phenomena.
In classical thermodynamics, thermal behavior concerns the relationships among temperature, internal energy, entropy, and heat transfer, as formalized by the laws of thermodynamics. These laws govern thermal equilibrium, conservation of energy, directionality of heat transfer, and behavior near absolute zero temperature. In this context, thermal refers specifically to energy associated with the microscopic motion and interactions of particles within matter.
