Link Spam
From Search Engine SEO SEM
Link spam is used to increase the ranking of certain target web pages by misleading the connectivity-based ranking algorithms in search engines. Link spamming refers to the cases when spammers set up structures of interconnected pages, called link spam farms, in order to boost the connectivity-based ranking, most frequently the PageRank, of one or a small number of target pages. The issue of link spamming is important not only because it can render significant gains in the rankings of target pages, but also because many instances of it are very hard to detect.
