The full phrase is, “Free as in speech, not as in beer.” It applies to software, especially 20+ years ago when FOSS software was coming into public view and people needed to understand what it was.

Some people would say “open source software,” but this struck others as a half-measure. The visibility of the source wasn’t the point, they would say. What matters is the freedom to do what you want with the software — https://www.gnu.org/philosophy/free-sw.en.html

If someone says “this beer is free” it means you’re charged nothing for it. If someone says “this software is free” it means (in this context) that you have an inalienable right to use it as you please — like you have an inalienable right to speak freely.