The dark web is an individual part of the internet that is purposefully concealed and not listed by regular search engines. To access it, you need special software like Tor (The Onion Router). The deep web is a part of the internet that includes all the stuff you can't find using regular search engines. This includes private databases, academic resources, and other types of content that need special permissions or credentials to access.
"Tor lives on the fringe of the internet and serves as the underlying technology of the dark web—a collection of hidden sites inaccessible via a regular browser and not indexed by search engines"
-International Monetary Fund