A(n) consists of nonproprietary hardware and software based on publicly known standards that allows third parties to create add-on products to plug into or interoperate with the system.

The answer is "Open System".

Explanation:

The term open system means a computing system, that integrated across software and hardware devices and provides complies with the same accessibility requirement.  

This connectivity and functionality mean, that a machine operating the Windows OS could be regarded as an open platform as can be seen by Windows being such a software OS. It is composed of the non-owned development tool, which is based on publicly reported values, that enable service providers to generate attach-on to the system.

First, what does the figure look like? i can't tell you what it is if you don't have one up it will make people confused and can't answer the question, not trying to be rude just stating a fact.