On Fri, Dec 18, 2020 at 09:46:38PM +0100, Emanuel Berg via Users list for the GNU Emacs text editor wrote:
> steve-humphreys wrote:
> 
> > This gets me to "defvar" [...]

> Just think of defvar as a way of telling Emacs and everyone
> else, "I intend to use a variable with this name."

Especially the "everyone else" part. You use defvar especially
when you want your package's users "hey, here is a knob you
can tweak to adjust the package to your needs...".

Cheers
 - t