The deep web is just that part of the network that isn't assigned IP addresses, sorta. That's about the only layer of privacy protection to it. Most of it is literally databases, and the like.
I reckon that's what we were talking about, as the darknet, those anarchic sites that deliberately avoid the 'surface web' and tend to lawlessness, is literally tiny. The deep web is huge, and the darknet is a itsy bitsy part of it.