mastodon.social is one of the many independent Mastodon servers you can use to participate in the fediverse.
The original server operated by the Mastodon gGmbH non-profit

Administered by:

Server stats:

336K
active users

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:

➡️ fedi.tips/what-other-kinds-of-

Whichever type you're signed up on, they connect together to form a social network called the Fediverse.

J.Kakaofanatiker💙💛

@feditips

What do you think about Meta joining it with Instagram Threads?

I think that on the one hand it's cool that it gives all kinds of non tech-savvy people easy access to the Fediverse, but on the other hand, many Threads users probably won't use it.

Another problem I see is that Meta could collect data about users on other platforms / instances like Mastodon when they interact with Threads users or vice versa which can happen unknowingly.