Originally a caddy was a gentleman learning the military profession by serving in the army without a commission.
In Scotland it is a person looking for employment, an errand-boy: from the French word cadet.
And the Wikipedia definition is: In golf, a caddy (or caddie) is the person who carries a player's bag and clubs, and gives insightful advice and moral support. A good caddy is aware of the challenges and obstacles of the golf course being played, along with the best strategy in playing it. This includes knowing overall yardage, pin placements and club selection. A caddy is not usually an employee of a private club or resort. They are classified as an "independent contractor," meaning that he or she is basically self-employed and does not receive any benefits from his association with the club.