Table tennis, also known as ping pong, is a sport in which two or four players hit a lightweight, hollow ball back and forth with rackets. The game takes place on a hard table divided by a net. Except for the initial serve, players must allow a ball played toward them only one bounce on their side of the table and must return it so that it bounces on the opposite side. Points are scored when a player fails to return the ball within the rules. Play is fast and demands quick reactions. Table tennis is the most popular racket sport in the world, with over 300 million active members of governing associations worldwide.