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The term Free Software is typically associated with software licensed under an FSF-approved license (The Free Software Definition), and the term Open Source (Software) is typically associated with software licensed under an OSI-approved license (The Open Source Definition).

Most of the applicable licenses are both, FSF- and OSI-approved. But there are exceptions. So

  • not all Free Software is Open Source (Software),
  • not all Open Source (Software) is Free Software.

Is there a term that includes both sets?

The alternative term FOSS, which stands for "free (and) open-source software", is, according to its Wikipedia article, for software that

can be classified as both free software and open-source software.

I guess that this applies also to FLOSS, which stands for "free/libre (and) open-source software".

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Just about the best term for it you have already mentioned.

FLOSS is a fairly widely-used acronym for software that is both free and open-source. You can also use FOSS, but there is an important note about FLOSS:

Libre, in French or Spanish, refers to 'free' in the way that we refer to it when saying 'free as in speech'. It means liberty, not lack of cost. Thus, if you use FLOSS as the acronym, you are technically implying that you could still charge for the software. FOSS could imply either. This is, however, a technicality.

I haven't found any single word that shows both free and open source.

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  • According to the quoted part from Wikipedia, FOSS only refers to software that is both (Free Software and Open Source Software). But I’m looking for a term that includes both sets, not only their intersection. So a term that can also be used for software that is Free Software but not Open Source Software, and vice-versa.
    – unor
    Commented Jun 24, 2015 at 10:42
  • @unor I'm not sure there is one. The intersection may be your best alternative.
    – ArtOfCode
    Commented Jun 24, 2015 at 10:43
  • 3
    Note that the combination can be read both ways. For example, "Software X is FLOSS" implies that X fits under both definitions. But when we say "Distribution Y includes only FLOSS", we generally mean that it includes free, libre, open source software inclusively.
    – mattdm
    Commented Jun 24, 2015 at 12:20
  • @unor "F(L)OOSS"?
    – Dan Getz
    Commented Jun 26, 2015 at 13:58
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The FSF has a process to approve licenses they consider free. OSI has a process to approve licenses that they consider open.

A requirement for the FSF to consider a license free is that it is open, so all free licenses are open source licenses.

But not all licenses that have been approved by the FSF have also be approved by OSI. Usually this is because they haven't sought out OSI approval. Does no OSI approval make it less open sourcy? I wouldn't say so. But it's difficult to be exact around vaguely defined concepts.

I'd say that in general, saying Open Source Software includes all Free/Libre software and more, so the term you're looking for is open source software.

If you only consider that software open source that has a license that has been approved by the OSI, this doesn't hold anymore.

There is no singular term for software that is licensed under a license approved by the OSI other than "software licensed under an OSI approved license". Nor is there a singular term for software licensed under a license approved by the FSF other than "software licensed under a FSF approved license".

So if you want the "fuzzy" definition (like F(L)OSS in itself is a fuzzy definition) just use open source software or OSS.

If you want to mean only licenses approved by the FSF or OSI, you'll have to go with the more cumbersome "Software under a FSF or OSI approved license"

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