I'm not sure either, but here's my guess.
When you take a course in England, you either get a 'letter grade' or you 'pass or fail'.
A letter grade means that you can pass the course at a number of levels. The levels run from A - G in most cases (especially GSCE courses), A = excellent, B = good, C = above average D = average E = below average and so on.
Pass or fail simply means that there is a mark that the student must achieve to pass the exam or course, for example 30 out of 40. If a person gets 29 out of 40, they fail the course and have to try it again to succeed. If they get 30 or more, the pass the course.
Student or Learner