"Open source" has more or less always meant something very specific as defined by the Open Source Definition. Adding restrictions on top like no commercial use or no lawsuits turns it into "source available".

It's how I intuitively read it too, even after decades of being exposed to tech, software, and licenses.

There's the OSI Open Source Definition, which is a free software definition.

I think the free terminology is clearer because free as in beer vs freedom is more obvious. Either it has a price or it doesn't. The Libre term is rather common alternative because of the ambiguity. The free as in beer or freedom is a common easy to understand explanation.

There's no such things for open source. In my subjective experience at least. "Source available" did not establish like Libre. Open is way more broadly ambiguous than free. And whether a license is open or open needs a full understanding and interpretation rather than only 'does it cost or can I use it for free.

Free is a dualist ambiguous differentiation. Open is broadly ambiguous and hard to verify.