Layer

A layer is the following:

In abstraction, a layer is an abstract place conceived as having depth.
In telecommunications a layer is an F region.
In telecommunications networks and open systems architecture (for example, the OSI model) a layer is a group of related functions that are performed in a given level in a hierarchy of groups of related functions.
In object-oriented design a layer is a group of classes that have the same set of (link-time) module dependencies to other modules, i.e. a collection of reusable components that are available for reuse in similar circumstances.
In archaeology, a layer is a body of soil-material, often containing artefacts, deposited at the same time. See stratigraphy.
Dual layer recording for DVD
Layers in 2D computer graphics
Layer de la Haye is a village in Essex, United Kingdom.
A layer can be a clonal offspring in the plant nursery business, produced by a reproductive technique known as layering.