A quality of being inadequate; a disadvantage, a fault.
A mark given for bad conduct to a person attending an educational institution or serving in the army.
A few of you have followed in the path of the perfect West Point graduate, Robert E. Lee, who never received a single demerit in four years. Some of you followed in the path of the imperfect graduate, Ulysses S. Grant, who had his fair share of demerits, and said the happiest day of his life was "the day I left West Point." (Laughter.)
That which one merits or deserves, either of good or ill; desert.