"To fail the course" means that a student did not meet the necessary requirements or receive the passing grade needed to successfully complete the class. Full definition
This could be things like lots of students failing a course, which could point to a problem in your course material. (elearningindustry.com)
There are also some students who failed a course because they weren't mastering any of the material. (laschoolreport.com)
4 - Students may pass a previously failed course because summer school might offer a different approach to learning the subject and a different teacher. (peoriastory.typepad.com)