Coming from IRC it always baffled me why people on Discord would talk about servers and channels too. Especially servers. It still irks me when someone says "Join my Discord server".

Calling them servers in discord always annoyed me. Spaces and rooms isn't much better. Room is fine, but space is incredibly nondescript.

Like the other replies you've gotten, I never really liked "server". It implies something very different from what it is.

Rooms is pretty obvious and straightforward, I think. And to be honest I rather like Spaces too. It's a lot less immediately clear, but there's something ineffable about it that just feels right to me. I'm just glad to see the old Communities feature (which was their now-deprecated first attempt at a Discord-like functionality) is hard to even find out about now. When I first joined I was confused about the difference between Communities and Spaces and had to search to figure out which to use, but when checking now to remember what the old one was called, I found it hard to even find the name of it.