Enthalpy is a thermodynamic potential that represents the heat content of a system at constant pressure. It is a state function, meaning that the change in enthalpy ($\Delta H$) for a process depends only on the initial and final states of the system, not on the path taken between those states. This concept is crucial for determining the amount of heat absorbed or released during physical or chemical transformations. For instance, changes in enthalpy are used to calculate the heat of reaction, the heat of fusion (for solid-to-liquid phase changes), and the heat of formation. The measurement quantifies the heat required to change the temperature or phase of a substance under standard conditions.