For every form I've ever had to file with the IRS, there's a corresponding set of instructions. Those instructions inevitably have a definitions section and/or define the terms in-line.
The instructions for form W8-BEN-E are at [0]. The definitions section starts at printed page 4 and continues through to printed page 7. Some terms you mentioned (like "Excepted territory NFFE") are not in the definitions section, but are described in their own sections.
I'm definitely not going to claim that it's foolish to consult with a tax lawyer (or similar such thing) when one is significantly uncertain about one's taxes. I'm definitely going to object to your implied claim that the IRS dumps a bunch of jargon on you and leaves you to rely on general-purpose search engines to figure out what the fuck they're talking about.