Brush class means that you don't have enough class hours, so you can only increase the class hours by accumulating class hours. . Brush hours mostly exist in universities, and many courses are online courses. Online courses must reach a certain amount of class hours to take the exam. Some students are not satisfied with the amount of class hours, so they can only brush the class hours, that is to say, open the webpage on their mobile phones or computers, and then continue to scroll the class contents until the class hours are full.