What is a rebound shell? What's the use of bouncing shells?

I'm sure you've heard shell, But rebound shell Have you ever heard of it ? What does it do ? Please see below ：
Simply speaking ,Shell Is the interface to implement user commands , Through this interface, we can control the computer , Like the ones that we see all the time ssh It's the execution Shell Command to control the remote server .
That rebound Shell What is? ? Its English name is Reverse Shell, What exactly do you do ? That is, the control end first listens to a certain TCP/UDP port , Then the controlled end sends a request to this port , At the same time, transfer the input and output of your command line to the control end , Thus, the control end can input commands to control the controlled end .
for instance , We have two mainframes A、B, We finally want to achieve in A Up control B. So if you use positive Shell, In fact, in the A On the input B The connection address of , Such as through ssh Connect to B, After successful connection , We can do that A Control by command B 了 .
If you use reverse Shell, That is in A Open a listening port first , And then let B De link A This port of , After successful connection ,A This side can be controlled by command B 了 .
rebound shell What's the usage? ?
Or the original example , We want to use A To control B, If you want to use ssh Wait for the command to control , That has to be input B Of sshd Address or port, right ? But in many cases , Due to the firewall 、 Security group 、 LAN 、NAT Wait for a reason , We can't actually connect directly to B Of , such as ：
A Although there is a public network IP, but B It's a machine on the intranet ,A You can't connect directly to B On .
B Firewall or security group restrictions are opened on ,sshd Service port for 22 It's closed .
B It's a dial-up host , Its IP The address changes frequently .
If B Being attacked , We want to make B towards A Report your situation , Then you need to B Take the initiative to connect A.
If this is the case , We can use rebound Shell use A To control B 了 .