P1.1 "Backlinks"
In search engine optimization (SEO), backlinks refer to hyper-links pointing to a particular Web page. Backlinks are important to SEO, because Google considers the quality and quantity of backlinks to determine PageRank.
Backlinks aren't the single determining factor for search rank, but they are a factor that's often abused for cheap boosts in Google search results. Google is constanly tweaking their search ranking formulas in order to weed out pages that earn their rank through cheap tricks.