In its most proper application, the term “server” means a component that provides a service that can be consumed by other technologies. I doubt that many people would contest that. However, it does include a qualifier that doesn’t enjoy such widespread acceptance: very rarely does a piece of hardware meet the definition. Almost everything that can accurately be labeled “server” would also most closely fit the definition of “software”. Firmware and embedded systems cover most of the rest. However, the big tower unit sitting in the back of your small office doesn’t really count. Neither do the “pizza boxes” filling datacenter racks. Yes, their manufacturers sell them as “servers” and almost all of us call them “servers”, but the term is technically incorrect in that usage.
Altaro’s HyperV blog has published an interesting approach on the various uses of the term server and how each use differentiates from the other. An informative and fun read: https://www.altaro.com/hyper-v/sysadmin-terminology-server/