@stefan It depends on the article.
"The" #fediverse is where we're talking now, a specific network of social-media sites that share not only a common protocol (#ActivityPub) but, more-importantly, a common core set of community goals, standards of behaviour, and moderation practices.
But just as there might be parallel universes, there can be parallel fediverses built around different goals, behaviour, and even protocols. In that case, you might talk about "a" fediverse.
@david_megginson @stefan
I would strongly disagree regarding the shared core goals.
#ActivitPub undergirds Gab, TruthSocial, Threads, and those are just a small number of the forks/feature-comparable Mastodon-like platforms. They share almost none of the goals, but are opportunistic and support reusing infrastructure others build & maintain for their own purposes, w/o contributing upstream.