It's most of the restaurants at CityWalk and a few of the sit down restaurants in the parks. It means if there is a line, and you flash your magic key, you get in.
But for places like Margaritaville, you'll still have to wait 20 minutes when it's packed. The regular people who walk up are told 1 hour. That happens at 8pm. It moves you up on the waiting list, sometimes to the top. Not really a problem if you have to wait, they give you a beeper and you walk around CityWalk taking pictures of family.