Safe to say you mean both. And you are 100 percent correct on it being super white.
Instances are like email servers. You are on Octodon.social. Mine is Kitty.Town. (this might help? it's a how-to https://medium.com/@GinnyMcQueen/toot-how-to-intro-to-mastodon-e5655bfa87d2)
The name for a specific Mastodon server is an instance -- a very programmer-jargony term. (Yeah, it's very tech-bro, here. We welcome and crave diversity!)
Just as I can be email@example.com and firstname.lastname@example.org, your Mastodon server is octodon.social, and nobody else _on your server_ can have the Lexialex username... but someone could create the same username on kitty.town.
The How-To that Ginny linked to you is a great resource, and feel free to ask for any clarification.
@Lexialex @starbreaker @GinnyMcQueen I found out about this after joining as well! The link is a great summation of Mastodon. Instances are groups under the Mastodon umbrella, so there's no one Mastodon location like Twitter or Facebook. I think using hashtags will allow us to communicate and connect with anyone using Mastodon in any Instance/group. @CobaltVelvet runs this group and looks to be doing a pretty good job! https://octodon.social/about/more
@webistrying @Lexialex @starbreaker @GinnyMcQueen @CobaltVelvet In my experience, this isn't something you need to think about much. Instances can have their own rules, and sometimes following someone is more technically awkward than it should be, but that's about it in terms of how decentralization affects daily use.
@Lexialex @starbreaker Imagine a big group of friends and family goes out to dinner and reserves a big table. Imagine several other big groups ALSO book the same restaurant. They all arrive at various overlapping times. Turns out you know the guy at the next table, so you start chatting. He introduces you to the person next to him, and you all talk. This happens all around the restaurant.
Mastodon is the restaurant, the different reserved tables are the instances.
I understand that @gargron and the other developers are working on this, but until web hosting providers provide "one-click" installs for Mastodon the way Dreamhost provides them for stuff like WordPress, you'll need some sysadmin skills to set up your own instance.
Octodon is a nice general purpose instance.