Link Farm, Bad! But what is it?

Complex question and no short answer. The search engines KNOW people are out to manipulate the system and look at a couple of things to decide if your part of a link farm or not.

Intent is chief among them. So many people don't understand how obvious their intentions are when they put  a spammy type of links page up.

Relevant content on the site your linking to is one of the most important. You see most link farm pages have tons of links to unrelated topics and especially lack a description along with the link. Ever see a link page with over a hundred links on it? You should notice that rarely do those links go to related websites. And with AdSense sites on the rise, publishers have a standard links page that is identical on all their sites.

Say for instance you own 50 websites of various topical content, now link them all to each other, this kind of linking pattern is detectable and creates constitutes a reciprocal link farm especially considering its intent is them manipulation of Googles Page Rank.

There are a lot of sites saying join us and get 3000 instant links from our partners.  Sounds like a link farm doesn't it?