What is private blog network?

     A private blog network (PBN) is a network of websites created solely to link out to another website and improve its organic search visibility. The idea is the “feeder” sites will pass link equity back to the main site, which will boost its authority and, thus, its ranking power.

Private Blog Networks simply mean a network of blogs that are owned by one person or one company but the thing is google doesn't like when you manipulate ranking this is why they're banned things such as exchanging links or getting some spammy links or even now private blog networks basically,if you have a network of websites that are all linking to a money site that is going against Google's