What does it means, when google says "0 search results found"? Did google try to get relevant search results from every website it knows about before displaying 0 results?
It means Google didn't find any web pages in its index that it considered relevant for that search phrase. Pages that have not yet been crawled or are blocked (robots.txt, x-robots-tag, etc) obviously cannot be displayed because does not yet know about it. Pages that are filtered out of Google's index for any reason (low quality content, terms of service violations, etc) will not be displayed even if they contain the excat phrase.
I am assuming you are asking this question because you are trying to figure out why your pages are not being returned in Google's search result for very specific search phrases. You need to make sure they are not blocked to Google. Then you can see if webmaster tools reports any problems. If not, then those pages simply may not be indexed yet. To help remedy that you can submit an XML sitemap and I would also recommend an HTML sitemap, too, as it provides links to those pages which is a good way for Google to find them.