A layer is the deposition of molecules on a substrate or base (glass, ceramic, semiconductor, or plastic/bioplastic) .
High temperature substrates includes stainless steel and polyimide film (expensive) and PET (cheap).
A depth of less than one micrometre is generally called a thin film while a depth greater than one micrometre is called a coating.
A web is a flexible substrate.
References
Layer (electronics) Wikipedia(Text) CC BY-SA