In Relative Grading System:
When a student could pass a class with an 'A' after having mastered only 40% of the material so long as that 40% placed them in the top of their particular class as made up of those particular students in that particular semester/section.
Conversely, a student in a class made up of other individuals taught another semester/section who has mastered 80% of the material might end up with an 'F' for the class if the rest of the students in the class all mastered the material at a higher level.
So ultimately, if the assumption fails, sometimes student who has scored less than pass percentage i.e. 35%, say he/she has scored 25% also could stand in "A" grade. Thats what it meant.