PN is short enough to fit several meanings, so I would rather understand the context than choose an expansion myself. An education website should make its subject and intended audience visible early on. That is what I would look for around [PN education website](https://pn.edu.pl). I like clear labels that tell a reader why a section may be relevant. A brief name can work well once the surrounding explanation gives people a sensible starting point and a way to ask a more specific question.