Big Idea - The Invisible Web
A discussion about search tools would not be complete without a mention of the "deep Web."
The deep or "invisible Web" is where billions of documents and rich resources are housed.
Searching on the Internet can be compared to dragging a net across the surface of the ocean; a great deal may be caught in the net, but there is a wealth of information that is deep and therefore missed.
The deep Web is where you can find many subject-specific databases and catalogued articles that will not appear in a surface search of the Internet.