FLOSS and FOSS
by Richard Stallman
The two political camps in the free software community are the free software movement and open source. The free software movement is a campaign for computer users' freedom; we say that a nonfree program is an injustice to its users. The open source camp declines to see the issue as a matter of justice to the users, and bases its arguments on practical benefits only.
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.
Thus, if you want to be neutral between free software and open source, the way to achieve that is to say “FLOSS,” not “FOSS.”
We in the free software movement don't do 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”.