Link bidding is a form of Internet marketing where a website owner bids on other websites to post a backlink to his/her website.
A link bidding directory offers webmasters a way to gain exposure for their sites. Websites being bid on are often grouped into categories (e.g., entertainment, finance). The position/rank for such websites is determined by their frequency of bids, where the highest-ranking websites have the highest number of bids.
References
Link bidding Wikipedia(Text) CC BY-SA