It's an unfortunate side effect of FSF's fascination with being uber-precise around terms like "free" and "open". Because English doesn't offer sufficient nuance here, and Stallman really, really hates it when people get the implications that were not intended, he had to go look for, or create, a word that would be unambiguously "free as in freedom" (by FSF definition of freedom, anyway). And so he did - with the unfortunate side effect that no English speaker outside of that community knows neither the word nor the meaning.