Is there a clearer more understandable word? Your definition of 'distribution' sounds like something much more specific (changes to binaries?) than mine.
Can found more explanations on reddit for the bravest :-)
I can only guess at the reason why Spacemacs team chooses this term, but there is one simple problem with it.
Users of Spacemacs are encouraged (by this naming quirk) to treat it as somehow essentially different to Emacs. That's wrong.
It would be of benefit to all for the code that comprises Spacemacs (layers mainly) to be released as packages. It would place greater emphasis on Emacs as the actual core product, and allow people to use and collaborate on smaller chunks of Spacemacs, without the monolith problem.