Emacs's Key Notation: What's the difference between "<return>" and "RET"?

What's the difference between emacs "<return>" and "RET" key notation?

"<return>" is the Return ↩ key while emacs runs in a graphical user interface.

"RET" is the Return ↩ key while emacs runs in a terminal.

"RET" is also equivalent to "C-m" (【Ctrl+m】). (For why, see: Emacs's Key Syntax Explained)

if you define:

(global-set-key (kbd "<return>") 'backward-char)

and run emacs in terminal, your keybinding will have no effect.

you need to use:

(global-set-key (kbd "RET") 'backward-char)

But the problem is, by binding (kbd "RET"), you are also binding (kbd "C-m"), regardless you run emacs in terminal or GUI.

What's the difference between emacs "<tab>" and "TAB" key notation?

Same situation for "<return>" vs "RET".

Here, "TAB" is equivalent to "C-i".

Also, "ESC" is the same as "C-[".