The implement used to hit the ball in a game of pool or billiards is called a cue stick. It is a long, tapered stick made of wood or other materials such as carbon fiber or graphite. The tip of the cue stick is usually made of leather or other type of material, and it is used to strike the cue ball to set it in motion, aiming to hit other balls on the table and score points. The weight, length, and flexibility of the cue stick can affect the player's accuracy and control in the game.