Impacted courses are classes that have high enrollment demand and limited resources to accommodate this high demand from students. Because of this, impacted classes may be difficult to enroll in because a lot of people need to take them and during enrollment they quickly fill up. You can find a complete list of impacted courses.  The main differences between regular and impacted courses are the drop deadlines and restrictions. While you have until the end of Week 4 to drop regular courses, you only have until the end of Week 2 to drop impacted courses. Get more information about impacted courses.