PageRank is a ranking system employed by Google that uses a number to indicate how important your website is on the internet.  It works by method of pages linked to one another.  Every time a page links to another, Google sees that as a page giving away a point in favor of that page.  The PageRank value is based on how many votes or points the page receives from other pages.  Likewise a page with a higher value gives more points toward every page it links to, based on its own popularity being higher.  Those pages linked to are then deemed popular by association, in essence.  The amount of points or votes given away by any given page are unknown but are reflected in the page’s overall ranking.

PageRank works on a scale from 0-10, with 0 being the lowest and 10 being the highest.    Important to note as well is that PR (PageRank) works on a numerical system where each number is exponentially higher than the last.  So a PR of 3 is significantly higher than that of 2 in the way that 2x2x2 (8) is much higher than 2×2 (4), in fact it is double.  As a general rule you should aim for a PR of 3 or better for your website.

Another factor that influences PageRank is whether or not your website is rich in valuable content. The importance of PageRank lies in it being one of the ways Google uses to calculate where your website will rank in the Search Engine results pages or SERPs.
If you would like to learn more about PageRank in-depth,  read more on PageRank in this article by Ian Rogers.

If you are unsure of how your website ranks, there is a cool free firefox addon that will allow you to easily determine the PageRank of your site or any site you visit.

You can also check a website’s PageRank with this free tool.