This is reported by Stanford (https://bugsakai.stanford.edu/show_bug.cgi?id=1386):
A small thing and an easy fix. The text on the assignment types page says:
"Create or edit an Assignment Type to be used when creating assignments.
Assignment Types are comprised of a set of default values and sub-seclection of the assignment settings for a particular kind of assignment."
"sub-seclection" should say "sub-selection".