I understand that "server" is an abstract term and just means "something which provides a service", but most other uses of the word relate to something owned by the person operating it. E.g., if I run a Matrix server instance, it's mine to administer, manage, destroy, etc. If I start a Discord "server" it's a glorified chat room or set of chat rooms owned and maintained by the company.
Language is powerful and helps shape our world, and by redefining "server" to mean a segmented part of someone else's website, it's another nail in the coffin for the concept of real ownership.