What is PageRank?
PageRank is a link analysis algorithm patented and used by Google to measure and rank webpages in its index according to the relative importance each webpage has.
PageRank tends to be presented in two distinct instances, namely Real PageRank used by Google (backdoors), and Toolbar PageRank with values from 0 to 10.
Real PageRank has the same building principle as toolbar PR but its much higher, as a numerical figure (going up to milions), than the PageRank Toolbar scale of 0 to 10.
Basically, Google takes all the real PageRank values of every page in its index and separates them into these eleven different ranges.