characteristic length

in thin films
Synonym: characteristic scale
https://doi.org/10.1351/goldbook.C00977
The term characteristic length or scale refers, in general, to the parameter which characterizes the density profile (of a given physical quantity). The static (equilibrium) or dynamic character of a characteristic length must be specified. The terms out of plane and in plane refer to characteristic lengths normal or parallel to the @[email protected], respectively. Since @[email protected] 'thickness' and characteristic length correspond to various concepts, the current usage where an out of plane characteristic length is referred to as the @[email protected] thickness, is confusing and should be abandoned.
Source:
PAC, 1994, 66, 1667. (Thin films including layers: terminology in relation to their preparation and characterization (IUPAC Recommendations 1994)) on page 1674 [Terms] [Paper]