Fair score is a new concept introduced by oobgolf. It is a simple and fair way to compare multiple scores that accounts for difference in courses, pars, and player skill.

A key component to USGA handicapaing is USGA differentials. These are essentially the difference between your ESC Score and the score that a scratch golfer would record on the same course. It is calculated as follows:
((Score - Rating) X 113) / Slope

You can see your own differentials by clicking on the "handicap" link next to your index on your "my game" page.

USGA differentials are great because they allow two golfers to compare scores on completely different courses. One course might be a par 69, 5,300 yarder and the other a par 72, 7,100 yard course, but their differentials are still comparable due to the fact that the USGA rates every course with a USGA rating and Slope.

The problem with USGA differentials are that they don't take into account the skill of the golfer. For example if I (20 handicapper) shoot a 85, its a much better score than if Tiger Woods (+8 handicapper) shoots a 75. Commonly Net Score is used for this comparison. But net score is only usefull when comparing two scores on the same course.

Thus oobgolf is using the following formula:
USGA Differential - USGA Handicap Index = Fair Score