Function: define-key

In KEYMAP, define key sequence KEY as DEF.
KEYMAP is a keymap.

KEY is a string or a vector of symbols and characters, representing a
sequence of keystrokes and events. Non-ASCII characters with codes
above 127 (such as ISO Latin-1) can be represented by vectors.
Two types of vector have special meanings:
[remap COMMAND] remaps any key binding for COMMAND.
[t] creates a default definition, which applies to any event with no
other definition in KEYMAP.

DEF is anything that can be a key's definition:
nil (means key is undefined in this keymap),
a command (a Lisp function suitable for interactive calling),
a string (treated as a keyboard macro),
a keymap (to define a prefix key),
a symbol (when the key is looked up, the symbol will stand for its
function definition, which should at that time be one of the above,
or another symbol whose function definition is used, etc.),
a cons (STRING . DEFN), meaning that DEFN is the definition
(DEFN should be a valid definition in its own right),
or a cons (MAP . CHAR), meaning use definition of CHAR in keymap MAP,
or an extended menu item definition.
(See info node `(elisp)Extended Menu Items'.)

If KEYMAP is a sparse keymap with a binding for KEY, the existing
binding is altered. If there is no binding for KEY, the new pair binding KEY to DEF is added at the front of KEYMAP. (fn KEYMAP KEY DEF)