This work acquaints readers with the contemporary apparatus of chemical thermodynamics in the surface and colloid science. The J potential is a new parameter, which represents a series of thermodynamic potentials and is determined for fluid systems as a grand thermodynamic potential in combination with the product of a system volume and some pressure p′. A classification has been given with discrimination of the classical J potential (when p′ is an external pressure) and special J potentials (at other values of p′). For both classes, hybrid types of the potentials have been considered, when chemical potentials are chosen as variables for one group of components, while the number of molecules or moles is selected as such for another group. The main attention has been focused on the application of all considered types of the J potential to a system containing a planar thin film. In particular, a case has been analyzed in which the pressure in the mother phase of a thin film plays the role of p′. Resulting fundamental equations have been formulated in terms of the disjoining pressure.