Seems like they're called "servers" now. I imagine "guilds" felt a bit too gamer centric for them after they saw how popular their service was becoming.
I've been working on a simple bot for one of the servers/guilds I'm on, and the API endpoints as well as documentation still heavily uses the term guild.
> Guilds in Discord represent an isolated collection of users and channels, and are often referred to as "servers" in the UI.[1]
The service is still very gamer centric, Discord Nitro for instance gives you a game subscription. I really hope they’re not trying to become Slack, that will be the death of them.