A tennis ball is the yellow or white bouncing ball designed for the sport of tennis, designed similarly to a baseball, though they differ in color, weight and composition. Modern regulation tennis balls are kept under pressure (approximately two atmospheres) until initially used. This is one of the pieces of equipment used in tennis.
Modern tennis balls are generally made in a yellow or white color, which are the only colors approved by the USTA and ITF. Tennis balls must conform to certain criteria for size, weight, deformation, and bounce criteria to be approved for regulation play.