overriding-terminal-local-map is a variable defined in `C source code'.
Its value is

It is a terminal-local variable; global value is the same.
  • This variable may be risky if used as a file-local variable.

Per-terminal keymap that takes precedence over all other keymaps.
This variable is intended to let commands such as `universal-argument'
set up a different keymap for reading the next command.

`overriding-terminal-local-map' has a separate binding for each
terminal device. See Info node `(elisp)Multiple Terminals'.