There is no hard definition of a server. I think OP finds the fact that people use the word all the time when it doesn't mean anything confusing - they feel there is a load of secret knowledge that other people have that they don't. But a lot of the time people just use terms without worrying about whether they actually know what these words mean or not.

Any network enabled machine responds to network packets with other network packets. Is that a server? Does it have to encapsulate a 'service' in some way? What is a service? Is this a higher level concept than tcp? Maybe it has to be something useful to someone, whatever that means. So OK my client machine starts running iis, is it a server now? I just use iis to test my Web page as I develop it, no one else connects to it, well apart from Steve who helps me with testing, he connects to my machine and it serves up the pages. We could go on.

When someone says they don't understand something, make sure you do before telling them they should.