Google describes PageRank:

PageRank relies on the uniquely democratic nature of the web by using its vast link structure as an indicator of an individual page’s value. In essence, Google interprets a link from page A to page B as a vote, by page A, for page B. But, Google looks at more than the sheer volume of votes, or links a page receives; it also analyzes the page that casts the vote. Votes cast by pages that are themselves “important” weigh more heavily and help to make other pages “important.”

In other words, Google conducts “elections” in which each web page casts votes for web pages with hyperlinks to those pages. But unlike a democracy a page can have more than one vote and links from pages with high PageRank are given more weight (according to their ranking) and thus help to improve the targets’ PageRank.

See the PageRank of a page with the PageRank meter in the Google Toolbar (an advanced feature). The more green the higher the PageRank.

Compare the relative PageRank of your site with other related sites by viewing the green bar to the left of a website in the web page section (near the bottom of the page) of the Google Directory page. (If your site isn’t listed in the Directory, that’s another way to improve its PageRank. See www.dmoz.org/add.html.)

In the next section, Improving Your PageRank, I offer suggestions for how to improve the PageRank of your webpages.