Meaning:Be honest, it's usually what you have to shout after striking a golf ball – it's a warning to other people on the course that your misdirected ball may well land on their head any second now if they don't take cover.
Origin:The most popular theory on the origins of "fore" claims that golfers used "Forecaddies" to go on ahead and watch out for where their ball was heading. As soon as they hit the ball they would shout "fore!" to warn the forecaddie it was on the way. They did this partly because golf balls were a bit on the costly side, so they didn't want to lose them, partly because they didn't want to waste half the morning looking for the ball.
There is also a military-related theory for the term, one that had gunners shouting “fore!” to warn the men in front of them to keep their heads down, they were about to fire at the enemy. This was believed to have been an abbreviation of “beware before”.
Our favourite – but most unlikely – theory, though, is that “fore!” is actually an anglicised version of “faugh”, as in the war or road bowling cry, “Faugh a Ballach!” (clear the way!).