by Andrei Smith
In this article I'll try to demystify Link Popularity and PageRank, or PR, clarify some common misconceptions and tell you how things work, in plain English, with facts and examples. Link Popularity is based on the premise that people link to good sites, and if a lot of people link to your site, then it must be good. In plain English, if other sites are linking to your site, your site is popular, therefore it is useful and deserves a boost in rankings, so people can find it faster and easier.
Link Popularity is not specific to Google only, but was adopted by the vast majority of Search Engines.