The Fediverse consists of various social media instances and their members that can directly talk to each other via the ostatus protocols. Mastodon is the most recent - and currently most popular - of the various ways to do. One of the older ways is Gnu Social (hence 'Here be Gnus"). The Hellbird Imperium is a jokey name for Twitter.
Obviously the map is in the style of an overland fantasy map and doesn't include a load of instances but making it amused me and the peeps on Mastodon who saw it.
Oh and if you want to find me on Mastodon I'm https://tootplanet.space/@Shutsumon