Hey,
Recent threads have pointed out some long-standing doc language in initdb that could be made more precise, especially in light of the relatively recent addition of a glossary. Toward this end I'm attaching a patch that defines three terms: "bootstrap superuser", "database superuser" and "superuser". I didn't add any extra-glossary links for the later two but did for the limited-in-scope bootstrap superuser that is really only defined in initdb (actually, I suspect the authorization docs could use a link too but haven't gone looking for an appropriate place yet).
In passing I also changed a few places where the documentation says "database" when the thing being referred to is basically the file system data directory, which is a cluster-scoped thing.
I did some grep'ing, though another pass or two is probably worthwhile. For now I submit a preliminary patch for consideration and buy-in before trying to polish it up.
David J.