From Wikipedia, the free encyclopedia: On the World Wide Web, a link farm is any group of web sites that all hyperlink to every other site in the group. Although some link farms can be created by hand, most are created through automated programs and services. A link farm is a form of spamming the index of a search engine (sometimes called spamdexing or spamexing). Other link exchange systems are designed to allow individual websites to selectively exchange links with other relevant websites and are not considered a form of spamdexing.
On the World Wide Web, a link farm is any group of web sites that all hyperlink to every other site in the group. You still run the risk of being punished or banned by search engines. This could be seen as an "illegal" link popularity scheme.
This is a dangerous place, it is best not to let your site to link to this place, will be search engine penalties.
Link farms are pages that consist solely of links to other pages but fail to offer any kind of useful content themselves. Site owners typically place their links on farms to artificially boost linking popularity and thus rankings on sites like Google. Some link farms are automatically generated, while site owners manage others as a repository of reciprocal links.