From what I understand (my school didn't have it), deferred Rush is a Formal Rush process that takes place sometime after the school year has begun. For the most part, it's just like formal fall Rush at other schools, but it's just held later in the year to give the girls time to get use to college life and to give them an opportunity to learn a little bit about the sororities on campus. Personally, I prefer Formal Fall Rush because that's what I'm used to, but I know that deferred Rush works out well for a lot of schools.