What Is The Meaning of "Fore"

"Fore" is another word for "ahead" (think of a ship's fore and aft).  Yelling "fore" is simply a quicker way to yell "watch out ahead" (or "watch out before").  It allows golfers to be forewarned, in other words.

The British Golf Museum cites an 1881 reference to "fore" in the golf book, establishing that the term was already in use at that early date (the USGA suggests the term may have been in use as early as the 1700's.