What is meant by message forwarding

Okay, so let's say you set up a gmail email address, and a yahoo email address... You can tell the gmail to do message forwarding to the yahoo email address. That way, if someone sends an email to "bobsmith@gmail.com" It will go to "bobsmith@gmail.com" and get forwarded to "bobsmith@yahoo.com" thus allowing you to create a false front if you don't want to give people your real email address, or if you like the yahoo interface, but like the gmail spam filter, etc... And gmail and yahoo was just the example I picked, but it applies to anything. There's call forwarding for cellphones, im forwarding in aim (someone sends you a message on aim while you're offline, you receive it as a text message on your cellphone), etc...