B (80s) Solid: there may be a couple of mistakes on exams, or weaknesses in written work, but the basic ideas and comprehension of the material are correct. B is a very good grade in my classes.
C (70s) Average: there are some basic misunderstandings of the material because the student has not put enough effort into the work. Regular attendance, completion of the readings, and light engagement of the subject will earn you this grade.
D (60s) Deficient: there are serious misunderstandings in the work and/or little evidence of any hard work.
F (50s or less) Failure to even try.