Android Debug Bridge.
It's used automatically when programming android apps on your PC (it'll send the development app to the phone and tell the phone to run it), but you can also use it to run commands on the phone that it normally wouldn't allow, and can sometimes unbrick a dead phone.
It can't fix everything, but it gives you a lot more control over the phone than you'd get otherwise.
I upvote things I like, and don't want to be one of those people who comment "THIS!", but you did proper research and it didn't get the acknowledgement it deserved.
Thank you the for data, I found it insightful.