Deep Web: But, as the NSDL community well knows, there's much, much more to the World Wide Web picture than most citizens realize
However, often overlooked on the Web are vast resources that Yahoo! and Google crawlers cannot access. There are databases on the Web where crawlers cannot get beyond the front page. The part of the Web that is not crawlable is called the deep Web, in contrast to the part of the Web that is crawlable, which is called the surface Web.