I wrote this into an internal FAQ today:
Q: What does “open” really mean?
A: “Open” is used in a variety of ways. An “open” API is an interface that uses standard protocols, tools and models and that can be written to by customers and third-party developers. An API is not, by itself, “open source”. Open source describes a development model in which anyone at all is free to download, improve upon and, with the agreement of the developer community, contribute code to a particular project. It is common to use open source components, often from many different projects, as building blocks of a proprietary piece of commercial software. Increasingly, there are open source projects, including OpenStack and OpenDaylight, which seek to deliver a complete and wholly open solution.
I like it, but given how freighted the whole topic is, it seems rather daringly simple and straightforward. So, dear readers, what nuances, caveats and gotchas am I missing?