What if I don’t have an Escape key?
Type C-[ instead. This should send ASCII code 27 just like an Escape key would. C-3 may also work on some terminal (but not under X). For many terminals (notably DEC terminals) F11 generates ESC. If not, the following form can be used to bind it:
emacs-lisp
;; F11 is the documented ESC replacement on DEC terminals.
(keymap-set function-key-map "<f11>" [?\e])