Someone who creates web pages that are either full of links to junk, or full of links to other links to other links. Link farmers harvest popular search engine terms from search engines such as "free games" or "free ebooks" and include these search terms in their link farm. However, the page never has any actual content relevant to the search term. A link farmer is a more passive form of email spammer, but uses junk web pages instead of junk email.
Link farmers are an Internet lifeform that are just as bad as email spammers.