Surface Web vs Deep Web vs Dark Net vs Dark Web
Surface web – The portion of the World Wide Web that is freely, directly accessible, and searchable with standard web search engines.
Deep web – All the parts of the World Wide Web that are not indexed/searchable by standard search engines. Web mail (gmail, etc.), online banking accounts, contents behind a paywall, etc., are all apart of the deep web.
Dark net – An overlay network that can only be accessed via special software. (e.g. Tor, I2P, Freenet, DN42, etc.)
Dark web – Dark web refers to websites on a dark net. It is the World Wide Web of a dark net. Since dark web is the collection of websites on a dark net, it too requires special software in order to access it.
Overlay – A computer network that is built on top of another network
Search engine indexing – The collection, parsing, and storing of data to facilitate fast and accurate information retrieval.
Internet vs World Wide Web
Internet – "The internet is the physical network of network of networks, and so on."
World Wide Web – "The World Wide Web, or simply web, is a way of accessing information over the medium of the internet."