A film often thins gradually to a thickness at which it either ruptures or converts abruptly to an equilibrium. Rupture under these conditions characterizes unstable films, whereas transition to an equilibrium characterizes (meta)stable films.
Source:
PAC, 1972, 31, 577. 'Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry' on page 614 (https://doi.org/10.1351/pac197231040577)