Doesn’t FOSS refer to software this is both free and open source? Not a union of free software and open source software? My understanding is that if a piece of software is not both open and free then it is not FOSS.
EDIT:
From the wiki page:
Free and open-source software (FOSS) is software that is available under a license that grants the right to use, modify, and distribute the software, modified or not, to everyone free of charge. The public availability of the source code is, therefore, a necessary but not sufficient condition. FOSS is an inclusive umbrella term for free software and open-source software.