GooglePageRank parameter is dedicated to the calculation of different factors related to the authority of your site. In basic terms, it estimates the quantity, quality and relevance of incoming links for your webpages. The higher the PageRank the higher is a probability that the site has some quality backlinks.
The last Google PageRank update was in January 2011, so it’s been almost 6 months between updates. Until this year pagerank updates were pretty stable – usually you could see a new update every 3-4 months.
That pagerank update was related to the introduction of the new parameter in Google SERP placement algorithm known as Google Panda. January Google Panda update hit hard content farms, and it also affected many established article directories.