Indeed. In system administration terms, there is one or maybe two servers, by which I mean computers in a building somewhere doing useful work. In user terms, there is one server. That is, for one forum, there is one “place” which everyone shares. (I say this, because Discord uses the term “server” to mean something more like “place” or “territory”.)
A Discourse forum may have multiple “Categories” and in some ways you might think of these as different “places” - they might each have their own moderators, for example. But we don’t call these “servers”.
It is essential not to confuse Discourse with Discord! They are two very different kinds of software offering.