Notre Dame OpenCourseware is a website that provides free online classes to people around the world. It is a special kind of online learning system, because it is made specifically for Notre Dame, a university located in Indiana in the United States. The classes are provided either in video or audio format, and they are taught by Notre Dame professors and other experts. This means that you don't need to be a student of Notre Dame to access the classes, and anyone can learn from the courses for free. So, with Notre Dame OpenCourseware you can learn about all kinds of subjects, from math to history, for free, just by logging on to the website.