Table tennis, also known as ping-pong, is a sport in which two or four players hit a lightweight ball back and forth across a table using small rackets. The game takes place on a hard table divided by a net. Except for the initial serve, the rules are generally as follows: players must allow a ball played toward them to bounce one time on their side of the table, and must return it so that it bounces on the opposite side at least once. A point is scored when a player fails to return the ball within the rules. Play is fast and demands quick reactions. Spinning the ball alters its trajectory and limits an opponent's options, giving the hitter a great advantage.

The international rules specify that the game is played with a sphere having a mass of 2.7 grams (0.095 oz) and a diameter of 40 millimetres (1.57 in). The rules say that the ball shall bounce up 24–26 cm (9.4–10.2 in) when dropped from a height of 30.5 cm (12.0 in) onto a standard steel block thereby having a coefficient of restitution of 0.89 to 0.92. Balls are now made of a polymer instead of celluloid as of 2015, colored white or orange, with a matte finish. The choice of ball color is made according to the table color and its surroundings. For example, a white ball is easier to see on a green or blue table than it is on a grey table. Manufacturers often indicate the quality of the ball with a star rating system, usually from one to three, three being the highest grade.

More Info: en.wikipedia.org