It’s the definition defined by the organization that coined the term open source.

The concept existed before then, but that hardly matters when we are talking about the specific term.

They are the authority on the matter.

I do not mean FOSS as Stallman means it, when I am talking about Open Source, I mean exactly what the OSI means, because that is the widely accepted form of the term.

You can find the open source definition here:

https://opensource.org/osd/

No. AMD and intel both are fine. Nvidia has some issues, though it is getting better slowly there.