The supplemental index
Google has two indexes. The normal index and the supplemental index.
Google defines the supplemental index as a place where they put fewer restraints on sites they crawl. This is not a place you want to be. Website pages that are in the supplemental index only show up when Google can't find something in the main index. Google mentions specifically that your URL's can put you in the supplemental index. Try to use static looking urls like my-page.html. If you need to use dynamic url's try to keep the parameters down to 2 or less. Other ways to say out of the supplemental index are to have unique Titles and meta descriptions on every page. It is also important to have unique content on every page. Pages with just a sentence or two will often be added to the supplemental index. Try to have at least 300-500 words of text on the page that is unique to that page. If you go and generate thousands of pages with no content your site will not rank very well.
