Deep web is literally content that cannot be found with search engines like Google. Account details, subforums hidden from guests, and unlisted YouTube videos are all examples of deep web content.
The "dark web" is the encrypted network that exists between Tor servers and their clients, whereas the "deep web" is simply the content of databases and other web services that for one reason or another cannot be indexed by conventional search engines.
Deep Web, also known as “Deepnet,” the “Invisible Web,” the “Undernet” or the “hidden Web,” are parts of the Internet that are not considered part of the “surface web,” or the portion of the World Wide Web that is indexed by conventional search engines. Many deep web sites are not indexed because they use dynamic databases that are devoid of hyperlinks and can only be found by performing an internal search query.
I heard first time about this term but it reminded me of robots.txt in which we can set robot to disallow to index some content pages. Is that is the only method to involve your site in deep net?