Sometimes you may want to exclude a certain page from search engine results. Anything you want excluded from SE results, you can add to your robots.txt file (see http://www.robotstxt.org/ for how to use it).
Old pages that no longer exist will eventually go out of the index on their own, but for anything you want removed faster (whether it exists or not), you can use the URL removal tool in Google webmaster tools. If the page still exists, you will need to block it with robots.txt before Google will accept a removal request.
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