Do you know about the "Dark Web" or "Deep Web"?

Can you explain to me (a computer dummy) what the “dark web” is?

Yesterday my wallet was stolen. I quickly cancelled my credit card (thief tried to make 2 very large purchases at Target but couldn’t pass verification and was photographed).

My Medicare Part B card was in my wallet (I didn’t know that it has my SSN on it). My first thought is that I’m absolutely screwed (I still think that I’m screwed). So I purchased identity theft protection from “Experian®” and “LifeLock®”.

LifeLock said that it will monitor the deep & dark web forum for suspicious activity using my sensitive information. Kind of spooky. HA!