What does credit hour mean in the US education system? 

In the US education system, a credit hour is a unit of measurement used to quantify the amount of academic credit earned by a student for successfully completing a course.

Typically, a credit hour represents one hour of classroom instruction per week over the course of a semester (or a quarter in some cases). So, a three-credit course would involve three hours of classroom instruction per week over a semester or the equivalent amount of work in an online or hybrid course.

The number of credit hours required for a degree varies depending on the institution and the degree program. For example, a bachelor's degree typically requires 120-130 credit hours, while a master's degree may require 30-60 credit hours depending on the program.

Credit hours are used to calculate a student's course load, determine their academic standing, and assess their eligibility for financial aid.