Steve made a great video this week to remove some of the confusion about page rank, and what its importance is to SEO.? Essentially page rank is an algorithm designed by Larry Page, and used by all search engines, to determine the importance of specific pages on the web.? It assigns a numeric weight to each webpage on the world wide web based upon hyperlinks to that specific page.? The purpose of page rank is to measure the “importance” of each page .
In a nutshell, each and every page of content on the internet can “cast a vote” for other pages.? The algorithm uses these “votes” to calculate the overall importance of a specific page, and gives it a numeric page rank value from 0 to 10 (zero being the lowest and 10 being the highest).
When a site has links from a page with high page rank (PR 3, 4, 5 etc) those pages essentially share some of their page rank with the site they link to.? Therefore if you have links to your site from 10 to 15 pages that have a PR of 3-5, then the page rank of that page, and your site as a whole will jump dramatically.? 10-15 links from high page ranked pages can be equivalent to thousands if not tens of thousands of links from sites with a low page rank (PR Zero or PR One).
This explains the importance of link building with sites of high page rank in related fields, and why simple spam links from pages will 0 rank will do little to help your site.