Here is something slightly mind-boggling. To me anyway: When you Google your way through the web, you are really just scratching the surface of available information. It seems that there is a hidden internet basement as well where all the databases and archives reside. It is referred to as The Deep Web, or (scary music) The Invisible Web.
When search engines crawl all the web sites out there, they come upon a huge number of archives of information that they cannot search within. The library of information may have been deliberately constructed to stop outside search engines from peeking in, or it is simply a case of data being stored inside a database, into which one can only peek by entering a query into a search field. Since the different segments of information do not have their own web pages, they are invisible to web crawlers.
If you are someone using search engines to obtain facts, the information is such databases is typically what you would want to look for. Data found within the boundaries of a reliable source, such as a library database, is often more trustworthy than loose facts and rumors floating around on Googlable personal web pages.
This article explains it better. There are also links and links to links.
“Think about the Web as a vast library. You wouldn’t expect to just walk in the front door and immediately find information on the history of paper clips lying on the front desk, right? You might have to dig for it. This is where search engines will not necessarily help you, and the Invisible Web will.”
Discovered through this very informative article with more tips and links over at Lifehacker
Iceberg photo found through Google Image Search. If you own this image and object to it being used here, please let me know.