This varies by school. US medical schools have different standards and even different grading schemes. It varies from a 2 point scale to a 5 point scale and they call grades different things, ie Honors = 5 = A = Excellent = whatever other crazy schemes are out there. Some schools give the top grade to 50% of students some to only 10%.
The best way to find out what a grade means at your school is to check out an MSPE from a graduating class. They have to put what percentage of people get each grade. This is so residencies can detect grade inflation which is rampant at lower tier schools (applies to me). Contact your academic affairs office for the stats for your school.
Generally, Honors is the best grade at good schools and about 10% of students get it. Also, subjective grading is complete BS...