The place on the clubface that is the best place to hit the ball. All clubs are designed to produce the straightest and longest trajectory when the ball is struck with the very center of the clubface.

The term "sweet spot" is used to describe how far distant from this point the ball may be struck with nearly ideal results. The more off-center the hit, the more the ball will slice or hook. Incidentally, the club will also tend to vibrate more.