Open source is a more informative term for this than free software. Not all free software is open source, but all open source software is free.

Edit: I was not aware of the FSF's definition. I was using a definition of free software being software that you can use without having to pay for it.

I think you are mistaken; neither is a subset of the other. At the very least, there are licences which are recognised as open source by the OSI, but not as free by the FSF, and vice versa [1]. I think it’s more appropriate to say they are two fundamentally separate definitions with a massive overlap.

[1] https://spdx.org/licenses/

> Edit: I was not aware of the FSF's definition. I was using a definition of free software being software that you can use without having to pay for it.

That’s called freeware. Also, open-source software can be paid (with the caveat that if someone buys it, you must allow them to redistribute it for free).

> Not all free software is open sourc

Depends on which "free software" definition you're referring to.

The FSF definition of "free software" requires it to be open source.

You have recited a successful incantation to summon the Stallman acolytes.

To add an additional suggestion, gratis can also be used to refer to free as in free beer. Comes from a latin root and is common in spanish speaking countries to refer only to free of charge, and not as in freedom.