I'm pretty sure that selectives, whether or not they're called selectives, are pretty much in both MD and DO curricula. I think it differs more by school rather than degree.
An elective at my school is whatever you want and whereever you want, though it may be a medical / surgical elective. An example of a surgical elective would be doing a month of neurosurgery half way across the nation at a hospital that isn't affiliated with my school.
A selective is where we have 4-5 different rotation options at one of our school's core hospitals. For example, we have 1 selective that has to be an IM subspecialty (GI, nephrology, cardiology, etc).