There is the web and then there is the Deep Web. Like many things deep — the ocean, space, and commitment — you probably want to fear the Deep Web.

A good way to think of the Deep Web is to compare the web with the ocean. There is the ocean surface, which is a familiar place. People swim on the surface, they go boating, sailing, fishing, and it’s a very common thing. But there’s more to the ocean than its surface.

Beneath the ocean surface lies the briny deep, the unfathomable depths, and Davy Jones’ Locker. Scary stuff! Ditto to the web.

The term Deep Web was coined by computer scientist Mike Bergman. He describes it as the web pages that Google and other search engines skim over when they crawl the Internet for web pages to index. For example, information on airfares and flight schedules is available on the Internet, but such things don’t appear on a search engine. That’s because the information is part of the Deep Web.

The scary thing is that there is a lot of information out there about you in the Deep Web. Your school records, employment history, medical data, shopping habits — all that stuff is on the Internet, just not indexed by search engines that lack the time or ability to truly look hard enough to find it.

Of course, the Deep Web — also known as the Dark Web, Hidden Web, or Deepnet — isn’t going to be hidden for long.

There are emerging a new crop of search engines, many of which are pay-based, that can search the Deep Web. A free one that will frighten you is pipl, a people-search that probably coughs up more information about you than you’re willing to admit to.

Then again, one of the reasons so much information might be available about you is that you — yes you sitting there — coughed up that information about yourself voluntarily. When you Twitter something like, “I’m watching the game while my baby son is napping,” then you’re giving up some personal information. As soon as you post that private stuff on the Internet, it’s no longer private.

Welcome to the Deep Web!