A blog network is a group of blogs that are connected to each other in a network. 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 advertising revenue generated from online advertising on the blogs.
In the past, a common use for blog networks has been for Search Engine Optimization where a company or website could easily obtain many strong backlinks by posting content onto blog networks. However, in recent years, blog networks have become almost exclusively associated with unethical Black Hat SEO because Google has clearly labeled them as a type of manipulative SEO practice. Now, links from blog networks will commonly lead to Google penalties including significant loss of search rankings. As a result, blog networks have now lost popularity except in Back Hat SEO circles.