> I have always assumed it to mean the intersection of the two contexts. As in, necessarily copyleft.

It's the union.

Actually it's harder than that: it's the union, but I challenge you to find a license that is open source and not free, or that is free and not open source :-).

I think there is a difference in philosophy between two parts of the movement, but in practice, what we call "open source software" is the same as "free software" (in terms of licences).