A communication process usually needs at least two parts. In order these parts to communicate, they have to speak and listen to others. In network we use to call what speaks a client, and who listens a server. In reality, like in real life, when two parts communicate, they act both as a server and as a client, while both are listening and speaking in order to talk. So, here, now, we're gonna call me and this host as `the server`, and you and the device you use as `the client`.