The rank of a page, called PageRank, is the result from a "ballot" among all the other pages on the WWW about how important a page is. A hyperlink to a page counts as a vote of support. The PageRank of a page is defined recursively and depends on the number and PageRank metric of all pages that link to it. A page that is linked to by many pages with high PageRank receives a high rank itself. If there are no links to a web page there is no support for that page.
(see full description at http://en.wikipedia.org/wiki/Page_rank).