The content that which you cannot find using the search engine is called as deep web. There are places in web that cannot be accessed by search engines but are accesseble if you have an address. 96% of the whole internet is Deep Web. All the content on internet that is stored at certain places like cloud or online repositories cannot be accessed by searches. These are accessed by addresses. These are know as Deep Web.
The data that are purposefully unrevealed and is not attainable through any standard web browsers is termed as Dark Web. Dark Web is mostly a place that is used for illegal activities. The content found inside Dark Web is usually found using the Tor network. Tor network is used for staying annonymos. Drugs trading, Illegal Paypal account details and many more things that one cannot even imagine, are available in Dark Web. Dark Web was invented for the purpose of US NAVY but now it's used as the black market of the Internet. This is how Dark Web becomes a subset of Deep Web that is used for illegal activities.