This is based on a variety of non-academic and outright prejudicial, financially motivated, elitist, and other often indefensible criteria:
-How much money the family might donate.
-How much ‘cache’ the university might get from having them (e.g. the daughter of a politician or entertainer).
-Whether they fulfill a political correctness quota/profile.
-Whether or not the applicant is connected to someone close to the board, administration, or powerful faculty.
-Whether or not the applicant has one of several specific pedigrees (ethnic, religious, private education at pedigreed school, time spent in Europe or other non-American locations, etc.).