Richard Fontana

CC BY-NC 4.0 is not an open source license, and by not permitting commercial use it is inconsistent with open source principles. I would suggest that this article be revised to clarify this point; this is not an "open source" violin.

The "Licensing" paragraph says::

"What’s the difference between open source and free and open source software? The difference is that the free license always requires that you share what you do under a free license. So, if you’re under an open source license and you make a modification you can change the license. If you’re under a free license you don’t have that option—the license must stay the same."

This distinction between 'free' and 'open' is nonstandard. Open source and free software are essentially synonymous, 'free software' being an older and more politically charged term. The distinction described here seems to be getting at the difference between copyleft and permissive, the two main varieties of free software/open source licenses. Permissive licenses allow modifications to be under other, more restrictive licenses, but copyleft licenses require distributed modifications to be under the same license, in at least some circumstances, and oversimplifying somewhat. For example, the GPL is an open source license, but if you distribute derivative works of GPL-licensed software they must be licensed under the GPL.