Definition: Google uses a weighted form of link popularity called PageRank(TM). Not all links are created equal. Google differentiates a link from an important site (such as CNN.com) as being better than a link from Jim-Bob’s personal home page. The Google Toolbar (which is a free download from http://toolbar.google.com) has a PageRank meter built into it, to see which web pages are considered important by Google and which aren’t. PageRank scoring ranges from 0 to 10, 10 being the best. PageRank scores get exponentially harder to achieve the closer to 10 they are. For example, increasing your own homepage’s PageRank from a 2 to 3 is easy with not a lot of additional links, jumping from a 7 to an 8 is very difficult to achieve. The higher the PageRank of the page that’s linking to you, the more your site’s PageRank will benefit. The better your PageRank, the better you’ll do in Google, all else being equal.
FirstClickSEO Commentary: An excellent way to determine the strength of a domain. But, this is by no means a valid and complete indicator of ranking results. This is one of many factors.