Google Page Rank is an algorithm named after Google founder Larry Page. Page rank is a number between 0 and 10. The number is assigned by the Google Search engine to a page to indicate Google's opinion of the website's overall importance. This is similar to an Alexa ranking, but it is calculated much differently. A higher page rank is achieved chiefly by having inbound links from other pages with a high page rank.

In short, when you get inbound links from other websites with a high page rank, those other sites pass along some authority. This is true except when the page linking to you uses the nofollow attribute. The nofollow attribute basically says to Google "Yes I'm linking to this page, but I don't vouch for this site in any way".

Page Rank is understood as having exponential significance. This means that a site with a Page Rank of 2 is likely 100 times more important than a site with a Page Rank of 1. This continues up through the page rank assignments. A site with a PR 5 is 500 times more important and influential than a site with a page rank of 1.

Brand new sites usually start off with a Page Rank of zero except in the case where an old domain once had a site with Page Rank, and someone else bought it. When that happens, Google usually resets the Page Rank anyhow. Google is the only search engine that uses a specific measurement called "Page Rank", but other search engines are known to use algorithms to measure both influence and significance.