Deep Web

The Deep Web is the part of the World Wide Web you can not search on common search websites such as Google. The part you can search is called the Surface Web. The first person who used the term "Deep Web" was Mike Bergman, a computer scientist, in the year 2000. 
Some people think that "darknet" and "Dark Web" are the same thing as Deep Web, but they are not. Let's explain what they mean:
In common networks, the Internet Protocols (IPs) of all users are in most cases visible. The Internet Protocol is an important information that reveals, among other things, the location where the user is accessing the Internet from. In darknets, the IPs are hidden, invisible or very difficult to find. This makes many people access darknets because they do not want the others to know this information about them, such as where they are. In other words, they access darknets to have privacy. 
There are many reasons people want privacy in the Internet. One of them is to do things forbidden by governments, such as piracy (which means sharing files protected by copyright laws).