SSH the Definite Guide says
Suppose you want to forward a connection from your local machine to remote.host.net. Both of the following commands work:
$ ssh -L2001:localhost:143 remote.host.net $ ssh -L2001:remote.host.net:143 remote.host.net
The forwarded connection is made from the remote machine to either the loopback address or remote.host.net, and in either case, the connection stays on the remote machine and doesn’t go over the network. However, the two connections are perceptibly different to the server receiving the forwarded connection. This is because the source sockets of the connections are different. The connection to localhost appears to come from source address 127.0.0.1, whereas the connection to remote.host.net is from the address associated with that name.
What is "the address associated with that name"?
How is it different from "source address 127.0.0.1"?