See deep link
Sometimes, the "dark" Web is erroneously used to mean the deep Web (definition #3 below). See Dark Web
The deep Web is content that is not found on a Google, Yahoo! or Bing search because it has been coded to keep the search engines from indexing it. The total Deep Web content is considerably larger than the public Web ("surface Web").
Also known as the "invisible Web" and "hidden Web," viewing such content is accomplished by going to the desired website and typing the query into the site's search box. Countless sites make their content available to the public in this manner, and registration may be required. Such sites may be free or paid as well as password protected.
Deep Web content resides within databases on the site's servers and not within the actual Web pages. However, search tools do exist that can query deep Web content. See LexiBot
The Deep Web Is Much Larger
There is a lot more data contained in the deep Web than what is visible on the public Web.