It seems like in any case, use of "server" is generalizable or stable over situations where we have "an entity communicating requests to another entity which is

It seems like in any case, use of "server" is generalizable or stable over situations where we have "an entity communicating requests to another entity which is responsible for servicing those requests." The problem here is that the word is invoked so as to distinguish entities at different layers of abstraction (a physical machine, a "platform", a set of supporting libraries and runtimes, a process, a function).