A system of adjacent layers or monolayers. The term bilayer applies to the particular case of a multilayer two monolayers thick. Monolayers and multilayers may be alternatively named 'films' provided boundaries can be defined for them.
Source:
PAC, 1994, 66, 1667. 'Thin films including layers: terminology in relation to their preparation and characterization (IUPAC Recommendations 1994)' on page 1672 (https://doi.org/10.1351/pac199466081667)