A blog network, also known as a link farm, is a group of blogs that are owned by the same entity. A blog network can either be a group of loosely connected blogs, or a group of blogs that are owned by the same company. The purpose of such a network is usually to promote the other blogs in the same network and therefore increase the search engine rankings or advertising revenue generated from online advertising on the blogs.
In September 2014, Google targeted private blog networks (PBNs) with manual action ranking penalties. This served to dissuade search engine optimization and online marketers from using PBNs to increase their online rankings. The "thin content" warnings are closely tied to Panda which focuses on thin content and on-page quality. PBNs have a history of being targeted by Google and therefore may not be the safest option. Since Google is on the search for blog networks, they are not always linked together. In fact, interlinking your blogs could help Google and a single exposed blog could reveal the whole blog network by looking at the outbound links.
A blog network may also refer to a central website, such as WordPress, where a user creates an account and is then able to use their own blog. The created blog forms part of a network because it uses either a subdomain or a subfolder of the main domain, although in all other ways it can be entirely autonomous. This is also known as a hosted blog platform and usually uses the free WordPress Multisite software.
Hosted blog networks are also known as Web 2.0 networks due to their rise to popularity during the second phase of internet development, known as Web 2.0 when interactive social sites began to rapidly develop.