Reverse port forwarding is one of the most powerful features of SSH. This is most useful in situations where you have a machine which isn't publicly accessible from the Internet, but you want others to be able to access a service on this machine. In this case, if you have SSH access to a remote machine which is publicly accessible on the Internet, you can set up a reverse port forward on that remote machine to the local machine which is running the service.

ssh -R 8000:localhost:80 user@REMOTE_MACHINE 

This command will forward port 8000 on the remote machine to port 80 on the local machine. Don't forget to replace REMOTE_MACHINE with the hostname of the IP address of the remote machine.

Using this method, if you browse to http://localhost:8000 on the remote machine, you will connect to a web server running on port 80 of the local machine.