Advanced Placement is a program run by the College Board (makers of the SAT) that allows students to take rigorous courses that allow them to experience an intro-level college class while still in high school. Depending on how well a student does on the AP Exam, the class can also earn them college credit.
The College Board has strict requirements and and clear guidelines on curricular and instructional resources that must be in place for AP courses. This creates a high likelihood that AP courses are designed to meet the same clearly articulated college-level criteria in high schools across the state - across the nation - across the world. All AP courses are regularly audited by the College Board.
An AP class on a student's transcript signals stronger academic training, especially with high passing scores (4's and 5's) on the AP exams.
Because AP courses are challenging and require students to study for a comprehensive exam, they help students develop skills that will help them be successful in college.