A short explanation for the P2 instead of P3 as per the Principles, Practices and Patterns this wiki is about.
The reason for the P2 name is historical, or you may call it a bit of nostalgia.
The first wiki was invented by Ward Cunningham in 1995: c2.com AKA Portland Pattern Repository. And Wikipedia is one of the most popular wiki born from that idea. C2.com has been the cradle of the Agile community. And it has been a Community of Needs.
In memory of that C2 wiki and its spirit, instead of using P3 as a name, P2 has been chosen instead.
The engine that is hosting this P2 wiki the Federated Wiki that has also been created by Ward Cunningham.