I’m still wasn’t not sure of the topology of these spaces so I asked chatGPT. Here’s the gist of it (I edited and rearranged the reply):

• Fediverse is a network of interconnected social media platforms that are decentralized and based on open protocols.
• Mastodon is a one of the social media platforms within the Fediverse that resembles Twitter.
• Lemmy is also a social media platform within the Fediverse that is similar to Reddit.

The Fediverse is a network of interconnected social media platforms that are based on open protocols and standards. It’s like a collection of different communities that can communicate and interact with each other. These platforms are often decentralized, meaning that they are not controlled by a single entity or company.

Mastodon is one of the most popular platforms in the Fediverse. It’s similar to Twitter, but with some key differences. Mastodon allows users to create accounts, post messages (called toots), follow other users, and interact with their posts by liking, reposting, or replying to them. One of the significant advantages of Mastodon is that it is decentralized, which means that anyone can set up their own Mastodon instance (a server), and users from different instances can still connect and interact with each other. Think of it as many different communities hosted on different servers, but they can all communicate and share information with each other.

Lemmy is another platform in the Fediverse, but it is more similar to Reddit. It allows users to create communities (called instances) based on specific topics or interests. Users can join these communities and post links, text, or discussions related to that topic. Other users can then upvote, comment, and participate in those discussions. Like Mastodon, Lemmy is also decentralized, so there can be multiple instances of Lemmy running independently, but they can still interact with each other.