Khan Academy is an online education platform that provides over 2500 instructional videos covering a variety of subjects. The videos are designed for self-paced, mastery-based learning and are available in 23 languages. Khan Academy is often used by teachers to "flip" the classroom, allowing students to learn new material through videos at home so class time can be spent on activities, projects, and addressing individual questions. Teachers provide feedback that helps improve the quality of Khan Academy's growing library of instructional videos.