An important component of the USGA Handicap System is the "course rating." What is a course rating? In an article titled, "Course Rating Primer," it states:
The Course Rating...is the evaluation of the playing difficulty of the course for the scratch player and the bogey player under normal playing conditions. The effective playing length is determined from the measurement of each hole, adjusted for the impact of roll, wind, elevation changes, altitude, dog-legs and forced lay ups. In addition to the effective playing length, there are 10 obstacle factors evaluated on each hole for both the scratch player and the bogey player.
These are the 10 obstacle factors considered:
The Course Rating is calculated from the effective playing length and obstacle factors for 9 or 18 designated holes. The Course Rating is expressed in strokes to one decimal point and represents the expected score for a scratch player. The Bogey Rating represents the expected score for a bogey player. The difference between the Course Rating and the Bogey Rating is used in the determination of the Slope Rating.
A male scratch golfer is one who can "play to a Course Handicap of zero on any and all rated golf courses. A male scratch golfer, for rating purposes, can hit tee shots an average of 250 yards and can reach a 470-yard hole in two shots at sea level." A female scratch golfer can "hit tee shots an average of 210 yards and can reach a 400-yard hole in two shots at sea level."
Each set of tees on a golf course receives a Course Rating and a Slope Rating. You can read more about the Course Rating at the USGA website including the history.