What does heat represent in terms of energy?

Heat represents a change in thermal energy, specifically the energy transferred between systems or objects with different temperatures. When heat is transferred, it causes a change in the thermal energy of the substance receiving the heat. This transfer can lead to an increase in temperature if the energy is added or a decrease if energy is removed.

Understanding heat in this way is essential in thermodynamics, where the focus is often on how energy is conserved and transformed. Unlike a fixed amount of energy or a consistent energy level, heat specifically denotes the flow of energy that occurs due to a temperature difference. This concept highlights the dynamic nature of thermal energy as opposed to static measures like temperature or fixed energy levels.