All code is shared "under someones own copyright and terms". Whether you use pre-existing words or not doesn't define if its open-source or source-available. I can write a license right now that I maintain the copyright, and written with my own terms that complies with the OSD. We happen to have a collection of existing licenses that have been vetted, but it isn't a exclusionary whitelist.

I'll reiterate, "source available" can only be defined as not OSD code that is viewable. Everything else is entirely open to implementation and interpretation.

This is the largest problem with the term. This is in stark contract to examples like "Fair Source" which has a legal definition like the OSD, and a entity behind it stewarding that definition [0], while being a subset of Source Available. All fair source is source available, not all source available is fair source.

Yet, fair source doesn't fall into your definition of source available.

[0] - https://fair.io/