[FRPLG]

It is not a hard concept. Most of the web is hidden behind password protected sites. Or dynamically generated (meaning there is not a specific page but a system that takes a request from a user and makes the page based on it).

The vast majority of the deep web is boring corporate database stuff. The illegal element of it is a part...just like any community. There is not separate "deep web" internet...it's all the same essentially.

Now the dark web is sort of a subset of the deep web and it is essentially the "bad neighborhood". It exists on the internet like anything else but it may be concealed or protected via normal password methods or more sinisterly via non typical means of access like Tor network which allows both the content owners and requesters to be essentially anonymous in every way. That's where the criminal element spread their wings.