To emphasize that “free software” refers to freedom and not to price, we sometimes write or say “free (libre) software,” adding the French or Spanish word that means free in the sense of freedom. In some contexts, it works to use just “libre software.”
A researcher studying practices and methods used by developers in the free software community decided that these questions were independent of the developers' political views, so he used the term “FLOSS,” meaning “Free/Libre and Open Source Software,” to explicitly avoid a preference between the two political camps. If you wish to be neutral, this is a good way to do it, since this makes the names of the two camps equally prominent.
Others use the term “FOSS,” which stands for “Free and Open Source Software.” This is meant to mean the same thing as “FLOSS,” but it is less clear, since it fails to explain that “free” refers to freedom. It also makes “free software” less visible than “open source,” since it presents “open source” prominently but splits “free software” apart.
“Free and Open Source Software” is misleading in another way: it suggests that “free and open source” names a single point of view, rather than mentioning two different ones. This conceptualization of the field is an obstacle to understanding the fact that free software and open source are different political positions that disagree fundamentally.
Thus, if you want to be neutral between free software and open source, and clear about them, the way to achieve that is to say “FLOSS,” not “FOSS.”
We in the free software movement don't use either of these terms, because we don't want to be neutral on the political question. We stand for freedom, and we show it every time—by saying “free” and “libre”—or “free (libre).”
