What’s an instance?
An instance is a specific website running Lemmy or another piece of federated software. For example, lemmy.world and lemmy.ml are two distinct instances
What’s a community?
A community is the “sub-reddit” of Lemmy. Kbin uses the word “magazines”, but these are the same thing.
What are federations?
A federation is a group of instances sharing posts and activity data with each other so that it can be displayed to their respective end users. For example, I can post to a community on lemmy.world and then you will be able to see my post when you are browsing feddit.de.
Whats the difference between all these?
Let me know if you have additional questions based on my answers above.
What’s mastodon?
Mastodon is a piece of federated software that is built to look and feel like Twitter, similar to how Lemmy is built to look and feel like Reddit.
What’s Kbin?
Kbin.social is a website you can use to browse posts from the Fediverse. From what I understand, it is similar to Reddit as well.
What’s ActivityPub?
ActivityPub is the underlying protocol that Lemmy, Mastodon, and other pieces of federated software use to communicate with each other. This is how they notify each other of new posts, comments, upvotes, etc so they can stay in sync with each other.
Summary:
Mastodon — all the privacy
Twitter — pretty bad privacy
Threads — we know everything about you