(noun)In computer science, abstraction is a mechanism and practice to reduce and factor out details so that one can focus on a few concepts at a timeSee 'pedia def ( http://en.wikipedia.org/wiki/Abstraction_layer)

virtual programming buffers or software insulators that reside between the inner details of some individual resource and any external entity that may want to use that resource.

An abstraction layer (or abstraction level) is a way of hiding the implementation details of a particular set of functionality. Perhaps the most well known software models which use layers of abstraction are the OSI 7 Layer model for computer network protocols, Open GL graphics drawing library, and the byte stream I/O model originated by Unix and adopted by MSDOS, Linux, and most other modern operating systems.