That stands for "on-sale date." Today is the one for ABSENT FRIENDS. As I said, nothing really happens on this day, except that the book actually shows up on the shelves of bookstores. I went by a B&N in my neighborhood and by golly, it was there on the table! It's a very odd feeling, folks, to see a book I wasn't even sure I could FINISH, sitting at B&N, out there in the world.