Problem-Based Learning system. This is not a regular spoonfed system where you sit down in a classroom, listen to the prof, and take regular quizzes or tests.
At USC, teaching is done through cases. So they give you a set of problem, and they group you with some people, then your task is to solve the problem by all means you can (research on your own, ask the prof, etc). You meet at regular basis with your group to discuss the given case. Also, the professors are not there to teach you, but to guide you.
That's a very brief overview of PBL. The students are set free to do as much research as they can. They have all the time in their hands.. so much that I heard they party every weekend

. But this is not my reason to pick USC though..
Hope this helps.