Function: ispell-minor-mode

Toggle last-word spell checking (Ispell minor mode).
With a prefix argument ARG, enable Ispell minor mode if ARG is
positive, and disable it otherwise. If called from Lisp, enable
the mode if ARG is omitted or nil.

Ispell minor mode is a buffer-local minor mode. When enabled,
typing SPC or RET warns you if the previous word is incorrectly

All the buffer-local variables and dictionaries are ignored. To
read them into the running ispell process, type M-$

For spell-checking "on the fly", not just after typing SPC or RET, use `flyspell-mode'. (fn &optional ARG)