The tldr to my understanding is it’s a bunch of different instances of the same thing (but not necessarily the same thing) which all have the ability to communicate, share data and allow users to interact across instances. This is why sometimes you see an @serverxyz after a username. It means their home Lemmy is another instance which is federated with yours.

So as an example let’s say I decide I want to run my own Lemmy server. I can impose my own rules, language of choice, admins, I could sell adds, ban a type of content etc. I can choose which other instances I want to be friendly with or cut off and they can choose the same for me.

Maybe there is a problematic Lemmy or one that is set up to house hate speech. I could decide not to federate with that instance cutting them off from myself.

So I guess why is this good… a few reasons that I’ve only come to learn recently. First off if you don’t like an instance you go elsewhere that better aligns with your values or interests or has a certain community you want to be a direct part of. Maybe you speak a different language and want to join one that is primarily in your language of choice or any other number of wants.

This type of set up allows for that where as something corporately owned and ran by a single company you get what they give.

That’s not to say every Lemmy is ran by some benevolent admin who doesn’t have some ulterior motives. But I’d you find this is the case there is little reason to stay and tough it out.

That’s my understanding so far. I’m new here and learning more about this every day. Take it all with a grain of salt

Lemmy is built as an alternative to Reddit. Instead of a single website, however, multiple people can each set up their own Lemmy, each of which is called a Lemmy instance, or just an instance for short. This person becomes its administrator, or administrators if it a a group of people. The special thing about Lemmy is that you’re allowed to join subreddits, called communities, in other instances of Lemmy. This intercommunication between different instances of Lemmy forms a network of instances.

But how do the instances tell each other what’s posted in their instance, such that each instance have no trouble sharing information? Since they’re all Lemmy, they just need to pick a standard way of sharing their data. That standard, which we call a protocol, is called ActivityPub.

ActivityPub isn’t a new thing, nor is it unique to Lemmy. One very popular service that uses this protocol is Mastodon, a Twitter alternative, and, like Lemmy, you have multiple instances of Mastodon that forms a network with one another through the ActivityPub protocol. Mastodon has long been calling their network the Fediverse, and with its current popularity, the word Fediverse has, for most people, become the word for any network that uses the ActivityPub protocol for intercommunication.

We won’t go into details or cover everything about what a Fediverse is, but one very important feature is that the people who set up their instances have the power to join or not join the Fediverse. Each instance can in turn block other instances, which is called a defederation. No one has the power to tell every other admin to defederate any particular instance — it’s up to the admin(s) of each instance.