Except for free-floating bubbles, films have to be supported by frames, bulk surfaces
or other films. The transition zone separating these from the
film proper, always containing some bulk liquid, is called a plateau border.
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 613