A spherical object or entity: a steel ball. A spherical or almost spherical body: a ball of flame. Sports Any of various rounded, movable objects used in various athletic activities and games. Sports Such an object moving, thrown, hit, or kicked in a particular manner: a low ball; a fair ball. Sports A game, especially baseball or basketball, played with such an object. Sports A pitched baseball that does not pass through the strike zone and is not swung at by the batter. A solid spherical or pointed projectile, such as one shot from a cannon. Projectiles of this kind considered as a group. A rounded part or protuberance, especially of the body: the ball of the foot. Vulgar Slang The testicles. Vulgar Slang Courage, especially when reckless. Vulgar Slang Great presumptuousness. To form into a ball. Vulgar Slang To have sexual intercourse with. To become formed into a ball. Vulgar Slang To have sexual intercourse. ball up To confuse; bungle. on the ball Informal Alert, competent, or efficient: a teacher who is really on the ball. on the ball Informal Relating to qualities, such as competence, skill, or knowledge, that are necessary for success: a manager who has a lot on the ball; a student who has nothing on the ball. A formal gathering for social dancing. Informal An extremely enjoyable time or experience: We had a ball during our vacation.