What’s an instance?
A website hosted by some kind individual or group created to host data and interface with one of the specific fediverse applications (Lemmy, Kbin, Mastadon, Pixelfed, etc).
What’s a community?
This is a Lemmy-specific term. They are topic-specific boards hosted on instances, similar to subreddits on Reddit. The Kbin term for this same idea is magazines.
Example: For Lemmy, they are represented as “!community”, such as !pics. On Kbin, they are “@magazine”, such as @pics.
What are federations?
I haven’t really heard the word used this way, I’ve heard it more as an adjective or verb. This may take more than one line to explain because I literally had to see it to believe it.
To have one instance federated with another is to have them communicating with each other, so that users, posts, communities, etc on one instance can be read by uses on another instance. It’s how I can read all these Lemmy posts on Kbin and comment under them, because these Lemmy instances are federated with the Kbin.social instance I’m currently on.
What’s mastadon?
A federated version of Twitter.
Whats Kbin?
A federated web application that combines the link-aggregation of Reddit with the individual micro blogging threads of Twitter.
What’s Activity Pub?
It’s the current protocol to enable federation of all these sites we’ve been talking about. Federation is possible because all these sites are speaking the same language, and this is that language.
In addition to Lemmy, Kbin, Mastadon that use Activity Pub, we also have Pixelfed, Micro.blog, Nextcloud, PeerTube, and more I’m sure.
If you have any other questions, just ask!
I’d also encourage people to check the Lemmy explorer first before assuming a community doesn’t exist just because it’s not on lemmy.world. Https://Lemmyverse.net has a surprising amount of communities on it, split among so instances. We don’t want a bunch of clones.