What Is A Private Blog Network (PBN)?
To put it simply, a private blog network (PBN) is a set of site domains that you own. It does not matter if you host the blogs yourself or if the blogs are hosted freely through services such as WordPress. However, free blogs are not as good as their self-hosted alternatives, luckily, the latter alternative does not usually cost much.
Basically, you create a private blog network by purchasing expired domains that already had visitors, content, and backlinks. These domains cost a few dollars, just as much as you would pay to register a new domain.
PBNs differ considerably from public blog networks. With public blog networks, you can buy links and guest posts, but so can anybody else, which makes the odds that Google will flag these links as inappropriate monumentally higher. In fact, Google has been known to deindex links to public blog networks, which is why any blogger who wants to be on the safe side needs to rely on private blog networks.