Page Rank is the link analysis algorithm or Google system to rank the webpages.Page Rank considers external links to a webpage as votes.So obliviously a website having maximum high quality external links likely to have high Page Rank.
A page with a higher PageRank is deemed more important and is more likely to be listed above a page with a lower PageRank.The page rank is measured on the scale of 0-10.
The system is developed by the Google founders Larry Page and Sergey Brin as a part of their research project for a new search engine.Sergey Brin had the idea that information on the web could be ordered in a hierarchy by "link popularity": a page is ranked higher as there are more links to it
How to check the Page Rank:
The Page Rank of a website can be checked by using Page rank Meter in the official Google Toolbar.The more the green the higher the page rank.
You can also check the Page Rank using http://www.prchecker.info/check_page_rank.php .
Importance in SEO:
The Page Rank has a great importance when it comes to search engine optimization.To rank a new website in the search engines you have create some good quality backlinks.The backlinks from a good PR website to your website counts very good in seo.
Once you are able to rank your website in the search engines,traffic to your site starts coming through the search engines which is the goal of every webmaster.
To know how to get 5000 PR 3 backlinks click here