What is the “Surface Web”?
It is best to imagine the Web as an entire ocean: the surface web is the top of the ocean which appears to spread for miles around and is the easiest part of the ocean to see or "access". You can access the surface web using any of the main search engines (Google, Bing, Yahoo etc.). You are on the surface web for example when you are buying from Amazon or reading the daily news.
What is the “Deep Web”?
The Deep Web was also part of the web at its conception, and in simple terms, it is the opposite of the surface as it is anything that search engines cannot find. This is the key difference between the two in real data terms; sites on the surface internet are indexed for search engines to find, but the deep web is not indexed. Both are available to the public, but special software is needed to access the deep web.
What is the “Dark Web”?
The Dark Web IS part of the Deep Web, but it has one major difference in that it has been intentionally hidden and is inaccessible to normal web browsers. The technology to create the Dark Web was initially created (and still funded) by US Military Researchers in the mid-1990s to allow spies and intelligence agencies to anonymously send and receive messages. Named "The Onion Router", it was quickly coined with the shorter "Tor" with its name coming from application layer encryption within a communication protocol stack; many layers representing the layers of an onion.