Link farm or link spams are those web pages which stuff excessive keywords in their content to get backlinks and this is one of the Black Hat SEO technique. However, search engines track out such spam pages and ban them from their search results. Hence it is inappropriate to submit your link on link farms.
Link farming is the process of exchanging reciprocal links with web sites in order to increase search engine optimization. It is considered as black hat method of search engine optimization(SEO) because the content on the web sites linking to each other is often not related and is often of a very low quality.