The term “free software” is prone to misinterpretation: an unintended meaning, “software you can get for zero price,” fits the term just as well as the intended meaning, “software which gives the user certain freedoms.” We address this problem by publishing the definition of free software, and by saying “Think of ‘free speech,’ not ‘free thing/asset.’” This is not a perfect solution; it cannot completely eliminate the problem. An unambiguous and correct term would be better, if it didn’t present other problems.
Unfortunately, all the alternatives in English have problems of their own. I have looked at many that people have suggested, but none is so clearly “right” that switching to it would be a good idea. Every proposed replacement for “free software” has some kind of semantic problem—and this includes “open source software.”
The official definition of “open source software” (which is published by the Open Source Initiative and is too long to include here) was derived indirectly from our criteria for free software. It is not the same; it is a little looser in some respects, so open source supporters have accepted a few licenses that we consider unacceptably restrictive of the users. Nonetheless, it is fairly close to our definition in practice.
However, the obvious meaning for the expression “open source software”—and the one most people seem to think it means—is “You can look at the source code.” That criterion is much weaker than the free software definition, much weaker also than the official definition of open source. It includes many programs that are neither free nor open source.
Since that obvious meaning for “open source” is not the meaning that its advocates intend, the result is that most people misunderstand the term. According to writer Neal Stephenson, “Linux is ‘open source’ software meaning, simply, that anyone can get copies of its source code files.” I don’t think he deliberately sought to reject or dispute the “official” definition. I think he simply applied the conventions of the English language to come up with a meaning for the term.
Open source supporters try to deal with this by pointing to their official definition, but that corrective approach is less effective for them than it is for us. The term “free software” has two natural meanings, one of which is the intended meaning, so a person who has grasped the idea of “free speech, not free things/asset” will not get it wrong again. But the term “open source” has only one natural meaning, which is different from the meaning of what people thinks. So there is no explanatory way to explain and justify its official definition. That makes for worse confusion.
Another misunderstanding of “open source” is the idea that it means “not using the GNU GPL.” This tends to accompany another misunderstanding that “free software” means “GPL-covered software.” These are equally mistaken, since the GNU GPL is accepted as an open source license and most of the open source licenses qualify as free software licenses.