As requested by Lawls. It's a place where you can chat in real time or even use voice chat.
The server is permanent, but you might want to register your account otherwise those are temporary.
Note that it collects information as most sites do so go through the privacy settings and be careful what private information you share.
For example by default the app detects what games you are playing and shows them.
I don't use Discord normally so I'm still figuring out all the settings and stuff.
Important: No mafia spoilers of the current game!