AP stands for advanced placement. It's a bunch of courses that are supposed to be equivalent to college level ones. After the course you take this big big test in May that has 100 multiple choice questions and then a bunch of essay questions. You can get a score that is either 1,2,3,4, or 5.
If you get a 3,4,or 5 you have a good chance of getting college credit. The test isn't required, though. If you take enough AP you can even skip freshman year in college. Yah