In thermodynamics, a path function or state function refers to a property or quantity that depends only on the current state of a system, and not on the specific path or process taken to reach that state. Path functions are also known as point functions or state variables.

Examples of path functions include:

- Temperature (T)

- Pressure (P)

- Volume (V)

- Internal energy (U)

- Enthalpy (H)

- Entropy (S)

These properties are independent of the path taken by the system to reach its current state. For instance, the temperature of a gas remains the same regardless of whether it was heated slowly or quickly, or whether the pressure was increased or decreased along the way.

In contrast to path functions, there are also process functions or path-dependent quantities that depend on the specific path taken by the system to reach a given state. These include:

- Work (W)

- Heat (Q)

- Free energy (G)

Work and heat are process functions because their values depend not only on the initial and final states of the system, but also on the path taken between those states. For example, the amount of work done by a gas expanding against a piston depends on whether the expansion occurs adiabatically (no heat transfer) or isothermally (constant temperature).

Path functions are useful for describing equilibrium states and for performing thermodynamic calculations, as they allow for the prediction of the system's properties without detailed knowledge of the path taken. Process functions, on the other hand, provide insights into the dynamics and energy changes that occur during a specific process.