So here are some "Key Messages" from Microsoft's standards team circa 2003 (doing battle with the Australian parliament no doubt) [Emphasis added]:

• An open standard is a publicly available specification which details certain technical functionality that may be implemented in different products and services.  It is adopted in an open, consensus-based process and must satisfy other criteria for transparency, ease of access, and broad implementation as described below.



• Open standards exist to facilitate interoperability and data exchange across various products and services in a marketplace of multiple, competing implementations, while ensuring that certain minimum requirements are met.



• Other types of standards (e.g., “proprietary standards”) and market-based mechanisms exist and are currently used to facilitate interoperability.  However, open standards ensure the highest level of interoperability across the widest range of competing products and services.