Some history: The discussion that prompted the August 2020 terminology change is consolidated in http://savannah.gnu.org/bugs/?58933 (it started earlier on the email list, but that bug report contains links to the relevant email discussion).
One point made therein is that the original CSTR#54 term for \& was "non-printing, zero-width character"; the 1992 revision of CSTR#54 expanded that to "non-printing, zero-width filler character" (which seems more misleading than the original, since it does no filling and has nothing to do with the typographical concept of filling). "Zero-width space" was purely a groffism. The commit log for the change in question (http://git.savannah.gnu.org/cgit/groff.git/commit/?id=36b5c885) also contains a lengthy explanation for why the current term was chosen. No one, including its inventor, seems fully happy with it, but there also hasn't been an alternate proposal that everyone is happy with. "Zero-width space" is a nonstarter for its Unicode clash.
