Ispell is a fast, screen-oriented spell checker that shows you your
errors in the context of the original file and suggests possible
corrections when it can figure them out. Compared to UNIX spell, it is
faster and much easier to use. Ispell can also handle languages other
than English. Ispell has a long history and many people have
contributed to the current version--some of the major contributors
include R. E. Gorin, Pace Willisson, Walt Buehring, and Geoff Kuenning.

You can find a short description in the directory
/usr/share/doc/packages/ispell/.