1. In snooker , the colour ball worth 5 points, placed on the blue spot in the centre of the table. In some (especially American) snooker ball sets it is numbered "5" on its surface.
2. Also the blues. In the eight-ball game variant blackball , also known as eight-ball pool, a differently colored but otherwise identical replacement for the red group (i.e., what would be the solids in an American-style pool ball set ).