terminal – How to create behavior like the $HOME variable

I have grown to use the $HOME variable a lot. So if I type $HOME/ and hit TAB it will write out /Users/user/. If I do a partial $HOME/Down and hit TAB it will write out /Users/user/Downlaods. I love this. But if I go into my .bash_profile and create a var like TOR=’/media/torrents’, then do source /Users/user/.bash_profile and try hitting TAB after typing $TOR it does not do this behaviour.

Can someone help me understand why?