An abbreviation for "Free Software/Open Source Software". Useful in discussions of same in which one wishes to bracket the religious issue of which term is to be preferred.

ESR-ites prefer "Open Source software" so as not to be confused with freeware or communism. RMS-ites (or GNU-ites) prefer "free software" so as to make a statement. However, when it's just us chickens talking, we don't need the distraction of yet another flamewar. Thus, "FS/OSS".