In the simplest terms, page rank (PR) is how much of the Google toolbar for page rank that is filled in with green. If the page you are looking at has a PR1 then 1/10th of the bar will be filled with green. If it has PR4, then 4/10ths of the bar will be green. Mostly only Google gets all of the bar filled green for a PR10, which is the highest possible rating.

To get the Google toolbar, which has the page rank bar, go to http://toolbar.google.com/ and download Google's toolbar. It will sit on top of your browser. The toolbar will not only provide you with lots of Google resources but it will also give you the page rank bar so you can see the page rank of your site and also that of any other site that you visit it.

But what exactly is Google's page rank system? Well, Google doesn't tell us exactly. However, we do know page rank relies primarily on Google's algorithms for determining the "importance" of the site or individual pages. The higher your site's PR, the more often it will show up in the SERPs (search engine results pages).

I can't speak officially for Google, but what webmasters have learned is that page rank is based primarily on the links to your site (called backlinks) that determine for Google how important your site is.

Google relies on a fairly democratic system by using its vast link structure to determine a page's value. Very simply, if your page gets a link from another site, that's a "vote" for your site. The more votes, the better.

However, Google also analyzes where the "votes" come from. If your site gets links from high-quality, authority sites with high PR, then your site benefits more from links from those high PR site sites than from links from non-authority or low PR sites.

Furthermore, if you put your link on another site with thousands of other links to other websites, then just be aware that Google will take that into consideration and will give your link its relatively small slice of of the other site's PR divided amongst all of the other links, if the site has any PR at all. So putting your site's link on a page that has a lot of other links may not do you that much good.

It's just good business to always check the PR of the sites with which you may want to exchange links by using the Google toolbar. Also, be sure to check out the page the other site wants to put your link on so you know how many links they are publishing. Less than 100 links is what you are looking for and less than 20 links is ideal.

Also, realize that reciprocal links (where your site links to their site and they link to yours) is less valuable in Google's eyes than one-way links to your site.

Once you get the Google toolbar and start seeing the PRs of other sites, you will be able to see the sites that get good PR and be able to model your site after those. I can't stress enough the importance of having the Google toolbar ...