A solid black Billiard Ball, the only one of this color in a standard 15-ball set composed of differently colored solid and striped balls.
This ball is so distinct that it has lent its name to an entire Billiards game (eight-ball, where the object is to shoot into pockets balls of one type before doing the same on the 8-ball last) and has transcended outside the context of billiards into popular culture at large.
An oversized decision-making/fortune-telling device based on it is called the Magic 8-Ball.
