Every line of GPL code is opensource. Not every line of opensource code is GPL.

...GPL is an Open Source license as defined by the OSI. Free Software and Open Source Software have overlapping (but not 1:1) definitions.

This is correct. Here's the OSI's list of approved licences: https://opensource.org/licenses/alphabetical

You seem to be very confused about these things, though those misconceptions are common...

Ultimately Free Software and Open Source mean the same thing. They come from philosophically different viewpoints that they emphasize - free software tries to emphasize on freedom, while open source is more a technical approach and often comes from more business oriented people.

But in terms of what licenses actually qualify as either Open Source or Free Software - they don't differ. And the GPL absolutely is an Open Source license. The organization that made the term Open Source popular agrees: https://opensource.org/licenses/gpl-license

Yes, the GPL is an Open Source license. However Free Software is a specific kind of Open Source and it adds a number of restrictions not found in a typical Open Source license (BSD, MIT, Apache etc.)

To reference the original point, Business may be allergic to the GPL, but at the same love the wider set of Open Source licenses.

Free Software, and Open Source very much do not mean the same thing. Free Software is a subset of open source with an addional layer of very restrictive clauses. It is that extra layer that prevents GPL code being used by most business.

While the difference is based in philosophy, yes, that philisophical difference has a huge impact in how code is used in the real world.

You seem to think that software under "a typical Open Source license (BSD, MIT, Apache etc.)" is not Free Software.

Free Software Foundation disagrees with this view: https://www.gnu.org/licenses/license-list.en.html

I stand corrected. Perhaps my point (or my understanding) then is more subtle. Perhaps what I mean to say is that the GPL license comes with additional virility, not found in BSD et al.

Perhaps the difference is most noticeable in libraries (where I do most of my work). Using a GPL library in a commercial app is generally impossible, where BSD (or LGPL) etc is completely acceptable.

In my experience companies are allergic to GPL specifically, whereas other licenses - especially MIT and BSD are far more palatable, and are frequently used.

That is really my point. They will use and celebrate your code if they can use it to make money and give nothing back. If you place some restriction on it that forces openness then it becomes toxic waste to them. It is a one way street.