Enthalpy is a thermodynamic property that measures the total heat content of a system. It combines the internal energy of the system with the product of its pressure and volume. Enthalpy is often used in chemistry and physics to understand energy changes during reactions and phase transitions, such as melting or boiling. In practical terms, changes in enthalpy can indicate whether a reaction absorbs or releases heat. For example, in an exothermic reaction, the enthalpy decreases as energy is released, while in an endothermic reaction, the enthalpy increases as energy is absorbed. Understanding enthalpy helps scientists and engineers design efficient processes in fields like chemical engineering and thermodynamics.