The Fediverse is a network of thousands of independent social media servers of many different kinds.
The most popular kind is Mastodon, but it wasn't the first and isn't the only one. Some of the accounts you interact with are on other server types, e.g. @Iancylkowski is on Pixelfed and @theatticdwellers is on PeerTube. There are many Fediverse server types:
Whichever type you're signed up on, they connect together to form a social network called the Fediverse.
@feditips @Iancylkowski @theatticdwellers I should note that I seem to be encountering compatibility issues between mastodon and some other activitypub apps like pixelfed or peertube. I follow a peertube account but as far as I can tell I've not seen a single post of theirs show up in my timeline.
So it is also highly dependent on whether or not the software that runs the instance you're on even supports the types of data they receive.
@dragonarchitect @Iancylkowski @theatticdwellers
PT used to have federation problems on older versions, is the server for the account you're following on an older version of PT?
@feditips I'm not sure honestly.