Link Farm: a link farm is a disreputable technique used to increase the search rankings of multiple websites. The practice is designed to manipulate Google's PageRank algorithm, which uses editorial links as a way to determine how search results should be listed. In this system, websites are encouraged to create high quality sites with original content, which should cause other sites to link back to this site and elevate the better websites. However, this process takes time. Instead, some websites choose to create link farms, a group of sites which all hyperlink to each other in order to obtain and give editorial links. Link farms can be created by hand, but many are built using automated programs.
Building a link farm is considered a method of spamming a search engine's index, otherwise known as spamdexing. The technique began in the late 1990s as a way to manipulate the search engine Inktomi's reliance on website popularity to structure and curate results. Since then, the tactic has evolved to apply to Google's algorithms. While link farms, such as "free for all" (FFA) link pages, are considered Black Hat SEO, the practice can sometimes be excused or missed if the links are between relevant, comparable websites.