@loyalnewb@universeodon.com

everything listed on
https://joinmastodon.org/servers is mastodon. and some not on there are also mastodon. universeodon is mastodon. you're on mastodon.

mastodon is not a single site but software any willing admin can set up. that's why everyone's usernames are like email addresses. because there is no "one true mastodon" (despite how much eugen wants to push mastodon dot social as "the" mastodon)

(the real confusing parts begin when you encounter non-mastodon people talking to you. i'm not on mastodon for example)