What does "fore" mean in golf?

As a golf term, the word "fore" means that other players on the green need to watch out for the ball. Sometimes, the direction "right" or "left" is used after the word, especially during tournaments, to let people know from which direction the ball is coming.

A golfer yells this word when he is about to shoot or when he hits the ball in an errant manner or into a group of people he did not realize were in the area. The term is used out of courtesy and a desire to prevent someone from being hurt by the ball.