Page Rank is Googles way of showing the user a basic ranking of a webpage. The ranking is from 0 to 10 with 10 being the highest. To calculate page rank there are numerous variables involved but the most important in link popularity. So the more incoming links you have to that webpage the higher Page Rank you will have.

Page Rank is updated all the time but not visible to users. The visible Page Rank on the Google toolbar is only updated a few times a year. Normally every 3 months. There are a few ways that you can get a general idea of your Page Rank at all times. One way requires the site to be listed in the Google directory. It has become known that the directory lists in order of Page Rank. The directory uses current Page Rank data and not the visible one that only updates every 3 months. So if you have a site in the Google directory you can always get a general idea on what your current Page Rank is.