(n.) Also referred to as the deep Web, the term refers to either Web pages that cannot be indexed by a typical search engine or Web pages that a search engine purposely does not index, rendering the data “invisible” to the general user. One of the most common reasons that a Web site’s content is not indexed is because of the site’s use of dynamic databases, which opens the door for a potential spider trap.
Web pages can also fall into the invisible Web if there are no links leading to them, since search engine spiders typically crawl through links that lead them from one destination to another. Data on the invisible Web is not inaccessible; the information is out there-it is stored on a Web server somewhere and can be accessed using a browser-but the data must be found using means other than the general-purpose search engines, such as Google and Yahoo!.
