The part of a golf club] meant to strike the ball. Has gone through many incarnations in the 4 to 5 hundred years of the game's existance. In modern golf it is a forged or cast piece of steel or other metal (titanium, tungsten, etc.)with horizontal grooves. Different club makers have different claims for their club faces (more spin,less spin, more forgiveness (of bad swings), more distance, etc. et.al.). It is the most important part of the club head.