It's generally assumed that a computer network server, at least in the way we talk about it, is hardware first and software second. While it's easier to envision a computer as a network server, in fact, the server is a piece of software running on the computer. In its most strict definition, a server is anything that provides services to fulfill requests made to it. Therefore, someone who takes our order and brings us our meal in a restaurant is a server and, in the same way, software running on a computer that processes an SQL request on a database and returns the data to the requester is also a server. Regardless of the way you envision a server, for the sake of learning about servers, let's agree that a centralized computer running server software that provides services to a network is a server.
With that understanding, let's look at the...