The department is the name of the college, and the class is a specific class. For example, students in the administration class 15 of the School of Economics and Management, the department is the School of Economics and Management, and the class is the administration class 152 (which can be referred to as the administration class 152 for short). Every major will have an abbreviation, which can be used when filling in the class (for formal occasions, such as exams)

If you don't know your department/class, you can ask the head teacher or the head teacher. If you have difficulty contacting the class teacher, you can go to the school letter network to make an inquiry.