A golf handicap is a number that is used to make the competition between players of differing skill levels more even. The number is calculated using a complicated formula that takes into account the golfer's adjusted gross scores and the difficulty of the course. The lower the number, the better the golfer. A "scratch" golfer is one with a handicap of 0 or better.
When two golfers with different handicaps play together, this number is used to even the playing field. At it's most basic, if a person with a handicap of 2 plays against someone with one of 10, the first person cuts two strokes off his or her score final score, while the second person cuts 10 strokes off his or her final score. The scores are then compared to see who won.
For a golf handicap to be official, it typically has to be obtained through an organization like the United States Golf Association (USGA). The formula for figuring it out takes into account the difficulty of the course on which a round was played to give a more accurate representation of a golfer's skill level. To do this, the USGA assigns what is called a slope rating to each set of tees on each course.
The slope rating is also used to determine the number of strokes a golfer gets at a particular course. A person's golf handicap and the slope rating are input into a formula that determines the handicap the person will use for that course. This number can differ from the player's handicap depending on the difficulty of the course. Since not all courses have the same level of difficulty, this makes player handicaps more relevant to the course being played.
Handicaps can be used to level the competition between two players or in a larger tournament. In a tournament setting, each player's number is applied to his or her gross score, and the net score is used to determine the winner.
anon281589 Post 12 
My handicap is the clubs. I've never played it and it's too confusing a game to understand. 
titans62 Post 11 
@kentuckycat  Thank you for clarifying. I know that most courses have a computer system that allows them to automatically determine ones handicap and it makes it a lot easier to do so as opposed to simply crunching confusing numbers. What I am wondering about the handicap system is how they came up with such a way to determine it? Also, I feel like the handicap system is not as accurate as people think it is as it does not take into account the condition of the course, the weather, or even changes that have occurred to the course. I know the course I played at in college was listed as being an average course when it was built, but as
the trees have grown in the course has gotten a whole lot harder and does not accurately reflect how hard it is in their course and rating.
I am wondering how often does the USGA update the course slope and rating and what factors do they use to determine difficulty? 
kentuckycat Post 10 
@matthewc23  I will say those are big variations in score and handicap, but I guarantee that a lot of people will never understand how handicap works because of the formula that is involved to figure it up. The way a handicap is determined involves both he slope and rating of the course. The rating is what a scratch golfer is expected to shoot on the course in regards to the difficulty of the average course. The slope works in a similar way, as it measures how an average person should shoot at the course, but does not necessarily reflect the score they should shoot. I know that the average slope is 113 for USGA courses, which involves most courses that carry a handicap in the United States. With a formula prescribed by the USGA a person takes their score, the slope and rating of the course, and the average slope and somehow comes up with their handicap. 
matthewc23 Post 9 
@jmc88  You are correct. For a lot of courses the amount of shots you shoot over par is usually around what your handicap will be, with maybe a slight variation. However, there are really easy course and really hard courses that will actually make a large variation in your score and handicap. I once played an easy course and shot an even par 71 as a 0 handicap. One would think that I shot my handicap, but in reality when my handicap was figured up in regards to the difficulty of the course I wound up shooting 75, because the easiness of the course expected me as a 0 handicap to shoot 67! Same can be said for harder courses
as I once shot a 74 on a par 72 course, but because of the difficulty my aggregate score was 70.
Most of the time there will not be variations like this and one can say that their handicap is the same as their shots above par, but again that is not always the case. 
jmc88 Post 8 
Some people seem to have some misconceptions about golf handicaps. Although people do believe that golf handicaps only go as low as zero, that is not the case. It is possible for someone to get a handicap in the negatives, which merely adds shots to their final score, but this is only reserved for players that always shoot under the par of the course and gives them a competitive disadvantage, so there is no reason for someone to have a handicap if they are that good. Another thing that people think is handicap is determined by how many shots you shoot over par. Say you shoot an 80 on a course that is a par 70 one would believe their
handicap to be 10, but that is not the case and it is determined by a formula that requires both the course rating and the slope, which are almost always listed on the card, and any course that is USGA affiliated will have both a slope and rating.

anon273055 Post 7 
There, theoretically, is no lowest handicap as there are + handicaps (lower than 0). For example, most PGA touring professionals would carry handicaps of +5 to +10 or better, if their scores were posted for handicap purposes. The maximum handicap is 36. 
anon161434 Post 6 
Do you only use a handicap when there are two people playing?

anon154714 Post 5 
the lowest golf handicap is 0, and the highest golf handicap is unlimited. 
knotnevada Post 4 
so what is the lowest possible golf handicap? 
anon15886 Post 1 
what is the highest golf handicap possible? 