Well, Deepnet and Darknet are two separate concepts even though both terms will appear in similar situations.
simply Darkweb is the part of the internet which is hidden from the eyes of search engines(public people). such as websites without robots.txt is a part of the dark web.
The deep web is a different concept and is a different world owned by hackers, drug mafias, secret govt agencies and other secret services(weapon, drug,immoral traffiking). We can't browse the deep web with normal browsers like chrome or firefox.
the networks such as TOR networks is used to access those websites (onion sites )which are part of the deep web. Complete anonymity is the specialty of deep web and that is why black marketers concentrate on deep web
hope this helps
regards
Gamer