For a very long time I was in the impression that Open System product means the product can run in majority of the Operating systems (Windows, Unix, Linux and others). But in reality it tends more towards Unix Operating system.
The Real Definition is:
Open systems are computer systems that provide some combination of interoperability, portability, and open software standards. (It can also mean specific installations that are configured to allow unrestricted access by people and/or other computers)
