A list or database of valuable contact information, especially of people in whom one is amorously or romantically interested. I don't feel the need to be in a long-term relationship because I've got plenty of phone numbers in my little black book.
n. a book containing the names and addresses of acquaintances who are potential dates, usually put together by men. Am I in your little black book, or can you already tell that I wouldn’t go out with you?