What is Mastodon? It’s a decentralized, open-source social network based on GNU Social. What does that mean? It’s confusing and it doesn’t work very well! Whatever! It’s the hip, new, disruptive technology that’s taking the Millennials by storm! It might even replace Twitter. (No it won’t.)
There are actually several Mastodon networks that interconnect. I’m at social.targaryen.house, but you could join shitposter.club, or memetastic.space, or even anitcapitalist.party, and we can all still talk to each other! Wouldn’t it be better and less confusing if everyone was on the same server? I don’t know. Maybe.
By the by, I’m not sure that I trust Mastodon’s security. I would suggest using a different password than your usual one, if you join.