info emacs

The minibuffer has its own set of local keymaps; they contain various completion and exit commands.

minibuffer-local-map is used for ordinary input (no completion).
minibuffer-local-ns-map is similar, except that <SPC> exits just like <RET>. This is used mainly for Mocklisp compatibility.
minibuffer-local-completion-map is for permissive completion.
minibuffer-local-must-match-map is for strict completion and for cautious completion.
Finally, minibuffer-local-filename-completion-map and minibuffer-local-must-match-filename-map are like the two previous ones, but they are specifically for file name completion. They do not bind <SPC>.