Have you ever been confused by the terms "page rank" and "Google ranking"? Have you ever wondered whether you were being bamboozled by a marketing pitch that promised such and such page rank or so and so Google ranking? Would you rather have a high page rank and a low Google ranking, or a low page rank and a high Google ranking? The answers will all become clear in short order. Read on.
First let's discuss Google ranking (GR), because it is something that anyone who searches for things on Google regularly will have an intuitive feel for. Google ranking is search-term dependent. If I have a website that sells dog collars, and it comes up at the top of the Google listings when I type in the search term "dog collars", then it has a GR of 1 for the search term "dog collars". If, on the other hand, I type in the search term "pet supplies" and I discover that my website comes up as the third website listed on the second page of results on Google for that search term, then my website has a GR of 13 for the search term "pet supplies".
So when it comes to GR, the smaller the number, the better. If the number is 10 or below for a given search term, you will be on the first page of results for that search term. The best GR to have for a given search term is 1.
Google ranking depends in part on who is linking to you or mentioning you on the web, and it also depends on who is on how well your competitors are doing. So if one of your competitors (who also sells dog collars) suddenly gets mentioned in a bunch of news articles on the web, and those news articles point at his website, he will likely move to a lower (better) GR, and you may move to a higher (worse) GR.
Page rank (PR) is totally different from Google ranking, although PR is a number which is assigned by Google. Page rank as nothing to do with search terms. Page rank is a number between 0 and 10, which is an indication of how important Google thinks your website is to the world. Like the Richter scale for earthquakes, the PR scale could be thought of like a logarithmic scale of how important Google considers your web page to be.
Every web page has its PR assigned separately, so there is not one PR for an entire website. Only one web page (currently Google's main page, but it was Yahoo's main page until recently) is assigned a PR of 10. There are multiple websites (but only a handful) which home pages have a PR of 9. There are many more with a PR of 8. There are many times as many with PR of 7, and so on. The lower the PR, the more web pages have that page rank. The vast majority of web pages have a page rank of either 0 or "unranked".
The higher the PR of one of your web pages, the more important Google auditors the outbound links on that page, and the more effect those outbound links will have on both the Google rankings of a page your outbound link points to, and the page rank assigned to a page that page points to. If you have a high-page-ranked page (for instance if your page rank is 7) and you put a link on it pointing to a friend's web page (for instance a page with page rank 1 and a Google ranking of 100 for the search term "dog collars", the link from you will likely move him to a lower (better) Google ranking for that search term (possibly a GR of 30), and simultaneously increase his page rank (sometimes from PR 1 to 2).
The last thing that is important to mention about page rank is that links that point at you from "unranked" pages can actually hurt your Google ranking for search terms relevant to the page that is pointing at you. This is Google's way of doling out punishment to websites that pay for inbound links (for instance from monthly subscription paid Search Engine Optimization (SEO) services). As soon as Google detects that a page is hosting "paid" links, Google will reduce the page rank of the page to "unranked", and keep it there. So if you ever pay for SEO services, make sure there is some way to remove the links to you from pages that might get slapped by Google with a page rank of "unranked", because links from such pages can add up to hurt you.