What Is PageRank?
It is a system for ranking web pages developed by Larry Page and Sergey Brin when they are still at Stanford University. Here’s a short description of Google about PageRank.
“PageRank relies on the uniquely democratic nature of the web by using its vast link structure as an indicator of an individual page's value. In essence, Google interprets a link from page A to page B as a vote, by page A, for page B. But, Google looks at considerably more than the sheer volume of votes, or links a page receives; for example, it also analyzes the page that casts the vote. Votes cast by pages that are themselves "important" weigh more heavily and help to make other pages "important." Using these and other factors, Google provides its views on pages' relative importance.“
In short, PageRank is essentially a score (0 -10) which serves as your site’s value in comparison to other websites on the Internet. The number and value of links pointing to your website are two factors that can affect your PR. I don’t know how Google calculates PageRank but if you are interested in more information about PageRank I suggest that you visit other forums about their understanding on PageRank. You will find a lot of forums and resources on the internet or you can always refer to http://www.google.com/corporate/tech.html for more information about PageRank.