OK. So when I'm looking over various sites, and they get a "Page Rank" of 2 or 3 or whatever, what exactly does this mean? After all, isn't a site's Page Rank assigned according to keyword? If this was the case, then wouldn't a site have several Page Ranks? I'm just curious to hear how this is being interpreted by others.
Every page has its own pagerank. Pagerank is how important Google thinks a page or website is on a scale of 1 - 10.
PageRank doesn't show your position in the search engines for a specific term, it shows the relative credibility and reputation of your website as a whole. Additionally, it's just one factor that determines where you end up in the search results. In most cases, your home page will have the highest PR on your site, and content pages beneath that will get a distributed value.
Page Rank is simply the measure of link popularity - the quantity and quality of inbound links. And by "quality of inbound links" I don't mean "good site" vs. "bad site"... I mean whether the page that links to you itself has lots (high quality) or few inbound links (low quality). There are actually 2 page ranks ... The "real" page rank for a given URL is some potentially huge number that Google knows about but that you NEVER see. It is constantly updated every time Google crawls a page that links to your URL, discovers a new page that links to your URL, or discovers that a page which used to link to you no longer does. Each URL on your site that is in Google's index has an up-to-date "real" PR. The other page rank is the Google Toolbar page rank... Though it's the least accurate of the two PR values, it is the one that most people refer to when they talk about PR because it's the only one that they can physically see. It's a number from 0-10 that is some type of logrithmic scaling representing the real PR of the URL. For example, say the logrithmic scaling used to translate a "real" PR into a Google Toolbar PR is base 10. Then the "real PR" might map to the Google Toolbar PR as follows: Real PR -----------------> Toolbar PR 0-9 -------------------------> 0 10-99 ----------------------> 1 100-999 -------------------> 2 1000-9999 ----------------> 3 10000-99999 -------------> 4 100000-999999-----------> 5 etc. up to Google Toolbar PR10. As you can see, having a PR0 does NOT mean mean that your URL has NO PR. It means that you don't have enough PR to be considered a PR1. If your page has at least 1 followed inbound link from a URL that is also indexed at Google then it has SOME real PR value > 0. Every followed inbound links carries some amount of PR. You should also be able to see from the above that it's exponential/logrithmic meaning it takes more and more links... it's harder and harder... to get to the next Toobar PR. Once in a while (typically about every quarter but it sees to be even more frequently over the last 6 months) Google will take a snapshot of the "real" PR for every URL in its index. They will then run a process against all of the URLs in the snapshot to map their "real" PR to a Google Toolbar PR. Then they publish that as what is commonly called a "PR Update". It simply means they update whatever database the Google Toolbar is looking at with the new Toolbar PR. Suddenly everyone's PR changes in their Toolbar. Note that it is usually a few weeks between when the snapshot is taken of the URLs and their "real" PR, mapped to the Google Toolbar PR, and published. So by the time PR is updated the Google Toolbar PR is already weeks out of date. As more time elapses between that PR publishing and the next, the PR becomes more and more out of date. So your URL's PR may show as a PR1 in the toolbar when it fact it might have a real PR equivalent to a Toolbar PR3 (or visa versa). So take it with a grain of salt. If you don't understand what PR is or how it's calculated I would recommend 1st reading The Anatomy of a Large-Scale Hypertextual Web Search Engine which was Larry Page and Sergey Brin's initial blueprint for what was later to become Google. The wrote it while at Stanford. In section 2 of this document, they explain this thing they call page rank and explain how it works. Matt Cutts from Google's Quality Team recently explained how PR works in layman's terms if you can't quite grasp the formula's used in The Anatomy of a Large-Scale Hypertextual Web Search Engine document above.