layer

Also contains definition of: double-layer
https://doi.org/10.1351/goldbook.L03488
Any conceptual region of space restricted in one dimension, within or at the surface of a condensed phase or a @[email protected] The usage of the term '@[email protected]' for an adsorption layer is confusing and is discouraged. The term double-layer applies to layers approximated by two 'distinct' sublayers.
Source:
PAC, 1994, 66, 1667. (Thin films including layers: terminology in relation to their preparation and characterization (IUPAC Recommendations 1994)) on page 1671 [Terms] [Paper]