On a tty, the TAB key is usually not distinguished from C-i. Other environments (such as X), allows a distinction. Emacs, therefore, supports this as well.
The following changes the keybinding for the TAB key only:
(local-set-key [tab] 'tab-to-tab-stop)
This, however, changes the keybindings of TAB and C-i, whichever is appropriate.
(local-set-key (kbd "TAB") 'tab-to-tab-stop)
Here is a quote from the node “Named ASCII Control Characters” in the EmacsManual:
‘C-i’, make just one binding, for the ASCII character <TAB> (octal code 011). If you do want to distinguish, make one binding for this ASCII character, and another for the “function key”
‘C-i’(and likewise for other such pairs), because the terminal sends the same character in both cases.