Google PageRank - a numeric value, a measure of 'importance' of the page in the search engine Google. Depends on the number of extrnal links to this page and on their weight (importance). In other words, on the quantity and quality of referring pages. And if to speak the language of mathematics, then PR is the algorithm for calculating of the credibility of pages used by Google. PR is not a major, but is one of the supporting factors in the ranking of sites in search results.