Open source inherently means you can compile the code locally, for free. You can’t necessarily redistribute it, depending on the license, but I’m not aware of a “you can compile this source for testing and code changes only but if you use it as your actual copy you are infringing” license.
I am very much open to correction here.
Open source inherently means you can compile the code locally,
Open Source means more than that. It is defined here:
If you use the phrase “open source” for things that don’t meet those criteria, then without some clarifying context, you are misleading people.
for free.
Free Software is not the same as “software for free”. It, too, has a specific meaning, defined here:
https://www.gnu.org/philosophy/free-sw.html
When the person to whom you replied wrote “free software”, they were not using it in some casual sense to mean free-of-charge.
Most free software is also open source and vice versa, but not all, the difference usually lies in the licence, this stackexchange answer gets it pretty well
