"Secondaries" means secondary applications (as opposed to the primary application that you are required to complete when applying to one or more medical schools).
If a school is interested in you, usually they will grant you an interview and also send out another list of questions or ask you to be more specific why it is that you're interested in THEIR particular medical school. It's not a standard form and differs throughout the schools. Sometimes they're pretty straightforward and not too complicated, but sometimes they want you to write another essay or answer a whole lot of additional questions.
Understand?
