hi friends, What exactly is a "link farm"?
A link farm is a network of some low quality sites linked to each other and the main website. these low quality websites are generally fed up with plagiarized/duplicate content and they sustain almost zero authority value!
The question has been asked and answered on the forums before, and Adrian98 has summed it up. If you want more detail, there is plenty here or elsewhere on the web, so you can use your favourite search engine to find it.