Ordinary language is a blunt knife when it comes to these matters. So if one wants to "define" porn, I would commend him to the current usage of the term. As to whether it identifies a clear concept, my answer is no.
You know... I think this is a GOOD way to start many discussions..
Setting out definitions helps keep everyone's thougths on the same frequency.
Mismatched lingo just leads to garbled junk... generaly.