PR is short for 'Pagerank'. Since Google launched their web browser toolbar it's included a pagerank bar.

It can be downloaded for free here, and has proved a unmitigating success since it's launch over four years ago. It has also prompted other companies like Yahoo and MSN to create their own toolbars.

The pagerank bar goes from 1-10, with only a few sites on the Web achieving a perfect ten rank. The above toolbar is currently at rank 7. By hovering your cursor over the pagerank bar it will,

Generally speaking the rank of a page is determined by the number of other site linking into that particular web page, and also by the pagerank of those pages which are linking in.

If for example's sake Google decided to put a link from their homepage (pr10) to this page, then this page would probably gain a rank of pr7 or higher. Most likely a rank of pr8. Whereas if 100 homepage's with pr2 and below linked to this page, it would probably gain pr5-6 at the maximum. Therefore it's not always a matter of quantity, but quality.

The Pagerank bar also give an indication whether a webpage is not within the Google search results.

This can mean one of three things, no sites are linking into this page and Google cannot find it, Google has only just crawled and ranked the page, or worst of the three, Google has decided to penalise or ban the page in question.