Advanced Placement

Overview
''The Advanced Placement (AP) program is a curriculum in the United States and Canada sponsored by the College Board which offers standardized courses to high school students that are generally recognized to be equivalent to undergraduate courses in college. Participating colleges grant credit to students who obtained high enough scores on the exams to qualify.''

Source: Wikipedia

Important Points

 * AP tests can be taken by anyone, not just high schoolers.
 * AP tests are accepted by the Big 3 just like CLEP and DSST tests.
 * There are almost certainly tons of study guides at your local bookstore for the main AP tests.

Resources

 * Official AP website from CollegeBoard
 * Wikipedia entry on AP