The "F" (free), "L" (libre), and "OS" (open source) all mean the same thing, the acronym is just meant to make extra-sure to include all the ways people refer to that kind of software (last "S).
There is open source software that requires payment to obtain.
There is open source software that you are not free to do whatever you want with (non-libre)
There is software available at no cost which is neither open source or libre.
Just about every permutation of these 3 concepts has some actual example in the real world. Please do not promote the idea that they are in any way synonyms.
Like the other commenter said, the F in F(L)OSS does mean free as in speech, not necessarily free as in beer.
I've been in the GNU/libre/open source world since 1986. My experience is that the L (for libre) was added specifically because the english "Free" is ambiguous and too often interpreted as without-cost/free-as-in-beer/gratis.
Stallman wants people to say FLOSS to denote free software versus open source software, and my interpretation of this article is that he only deems the GNU licenses to be truly free (libre) software.
Simply has never been the case.
One example I am familiar with is an (old) project called LinuxSampler. It was (probably incorrectly) licensed GPL+modification clause that prevented its use in any commercial hardware project.
There have been some other projects that are released under what might be termed "GPL-but-no-military-use".
The people I know who have added clauses like this do not believe they are breaking the spirit of open source; I'm not here to insist that they are right or wrong.
And let's not forget, licenses are legal contracts, so it behooves people even more to get them correct lest they be sued.