PageRank

Google's PageRank technology uses an algorithm to determine search engine ranking for each page on a website. It uses more than 500 million variables and 2 billion terms to measure the relative importance of a page. Google.com: Technology Overview

Search Engine Optimization (SEO) is the process of adding keywords and links to a site in order to increase its search engine visibility. Some companies with popular sites sell links to sites with lower-ranked pages to falsely inflate the site's popularity. Google's official position is that sites discovered to be selling links will be ignored by PageRank, thereby making their links useless. Google Webmaster Help Center: Where should I report... In 2007, Google extended this policy to blogs with a high level of cross-linking. TechCrunch: Google Declares Jihad On Blog Link Farms (October 24, 2007)