Google PageRank is probably one of the most important algorithms ever developed for the Web. With billions of existing pages and millions of pages generated every day, the search issue in the Web is more complex than you probably think it is.
Google Pagerank was originally named after Larry Page, one of the founders of Google who developed Pagerank with Sergey Brin (the other founder of Google).
They had the idea that the more people that link to a page, the more popular it is. Over time this has evolved to include all of the factors which dictate where a page appears on Google’s search results, plus many more.
A pagerank is a number between 0 and 10 and essentially dictates how important the page is according to Google. Each link is considered to be a vote, but if a link comes to your website from somewhere Google does’t trust then it is ignored.
Not all links are considered equal, for example if a page that has PR2 has 3 links to other websites, and a page with PR 6 has 30 links to other websites the the links from the PR2 website will probably be worth more as the former have greater importance placed on them. It’s worth noting that you don’t “give away” your pagerank, you’re simply voting for whatever site you link to.
The other thing you need to know is that PR 10 is not 10 times the value of PR 1 – it’s logarithmic, not linear so it could be 100 times the value, but Google don’t share exactly how their system works to prevent people from cheating or “gaming the system” as it’s known.
If you want an in depth explanation of how Google Pagerank works, complete with equations, then I recommend checking out the article Google’s PageRank Explained as it’s the best in depth article I found, and well worth a read if you’ve got the time. Google updates the page rank that anyone can view approximately every 3 months