>I've also heard it used to describe projects that are open source by anyone's measure but have contribution or project governance requirements like for example sqlite.

Anybody calling SQLite "source available" is mistaken. Are you sure they weren't confusing "source available" with "open core" (Open Source + proprietary add-ons)? SQLite's source code is public domain, which meets the Open Source Definition and is true Open Source. But they also sell proprietary add-ons to fund its development:

https://sqlite.org/prosupport.html