Can somone elaborate the term defence

Hello there. Considering that you are asking this in reference with the admission in colleges, then defense is a separate category which is being made for the students who are dependent on parents and their parents are in army. Now under this category their comes preference to whom the seat will be offered first. Like for someone belonging to any martyr will get the highest preference, someone dependent on who has got gallentry award will be coming next in list. Then the preference is given on the basis of rank in the army and so on.