Page rank is a measure of how important your website is to Google. A page can have a rank between 0 and 10 (0 being the lowest rank). In fact a page can have no page rank at all, which means it hasn’t even been picked up by the search engine bots or spiders.
Note: Page Rank is not the same as your position on the search engine results page (SERP).
Page rank is calculated based on how many other web pages link back to your website, these link backs are considered votes, however not all of these votes are of the same worth. A link back page that is already considered important and has a good page rank is worth more than a page with a low page rank. Also, a page with lots of links is worth less to you than a page with only a few links… therefore the link backs that are most sought after are from pages with a high page rank and low link count. Here is the Wikipedia entry on Page Rank.
Sites with good page rank generally do better on the search results page than pages with poor page rank, however, if the content on the page is not right then it won’t make a difference how much page rank your site has. Also, the links that gave you the page rank should make good use of keywords in those links to let Google know what your page is about.
You can check a page’s Page Rank by installing the Google toolbar on your browser and customise it to show Page rank, this shows a little progress bar icon on the toolbar showing the current page’s page rank. You could also use a site such as PR Checker to check a page’s page rank.