Use only the left option key as meta key in Terminal.app

And, as I already answered you on stackoverflow, the solution is to put the following line into your ~/.bash_profile, which remaps the unicode character "∫" (Unicode: E288AB, which is what is sent to your terminal right now in your desired configuration when you press Option + °) to the backslash character:

bind '"\033\xE2\x88\xAB"':'"\\"'

Terminal.app is actually doing what it's supposed to: shift-TAB sends ESC [ z which Emacs reads as M-[ z. The problem is that the terminal description for xterm-color (the one usually used with Terminal.app and other terminal emulators) is missing the kcbt declaration, so Emacs doesn't know that that's what the key sends.

There are two ways to fix this:

1. Edit the terminal description:

   $ infocmp >xterm-color.ti
   $ printf '\tkcbt=\E[Z,\n' >>xterm-color.ti
   $ sudo tic xterm-color.ti
   

2. Tell Emacs about it directly:

   $ echo "(global-set-key "\M-[Z" 'something)" >>~/.emacs
   

The problem in both cases is that there doesn't seem to be a backwards-tab command to substitute for something. Emacs.app binds backtab to yank; what do you want it to do?