Google alongside its main index has a secondary one where less significant or duplicate web pages are put. This is the Google Supplemental Index. If you want to check whether one page from your site is indexed in this index you need to issue the following command in the google search box.
site:www.example.com *** -sup
Getting your pages out of this index can be very difficult. One way to do this is to check pages with similar content to yours and find what makes google like them more and adjust accordingly your own page.