It uses a slightly different configuration than Mastodon but otherwise it behaves exactly the same. You can read and reply to Lemmy posts from Mastodon.

In the same way, you can block requests from certain servers (this is called defederating) so their users can't reply, follow or spam you.

So, I'm connected to a fancy computer called a server, and so are you, but we're connected to different servers. The reason we can still talk is that despite being on different servers run by different people, those people have made it so that the servers can share what I say with you, and what you say with me.

Federation is simply a fancy term for an agreement to share something. In this case, it's our text posts.

There are other kinds of federation, but that's not important to Lemmy. Since you asked specifically about Lemmy, I'll leave it at that.

You're on lemmy.world and I'm on programming.dev, but we can still see each others posts and interact with each other because lemmy.world and programming.dev are federated.

You are on Lemmy.world. I am on Lemmy.ca. These are distinct websites but they use the same underlying service. Federating means that the two websites share their info - this let's us talk despite being on different websites.

Well, you're commenting on a Mastodon post...