Google, which is the gold standard for all page-ranking systems (including PageRank as it is called by the industry) was started by two Stanford University Students – Sergey Brin and Larry Page (no pun intended.) These two students (now billionaires) invented the Google algorithm now known as PageRank.
All PageRank is really is a formula, not unlike the FICO score that is used to calculate credit. Only in this case the formula takes in a lot of variabilities to see if a page is worthy of being included at the top of search engine rankings. This concept weighs a page's importance based upon the incoming links. In essence PageRank is a type of prediction, but one that can make a great deal of difference to the credibility of your business. It is the estimation of the likelihood that a given page will be reached by a web user who is randomly surfing the web. This popularity is measured by how an individual might have followed links from one page to another. This of course makes some links more valuable then others and it is your goal as a web master to use SEO techniques to make your links valuable in terms of the PageRank system.
Another genius element of the PageRank algorithm is that it keeps link results relevant to what the person is searching for. The fact that PageRank keeps searches on the Internet accurate (for the most part anyway) has made it the most emulated and popular algorithm in use by search engines today.
Of course the Google PageRank system is not invulnerable to exploitation. There are many ways of fooling the algorithm, usually through the buying and trading of links which is known as white hat SEO. There is also black hat SEO that as mentioned before uses techniques frowned on by Google to boost a web page’s rankings in the search engines.