A Dragon Ball is a magical artefact that belongs to a set of seven, and when united with the other six have the power to summon forth a dragon god, who will then grant a certain amount of wishes to the user. They are the namesake to the series and centric to it's importance.
A Dragon Ball is golden orange in colour, with a darker red star floating in the middle. The amount of stars inside range from 1 to 7 and signify which of the set it is.
There are 14 Dragon Balls, 7 on Earth and 7 on Namek. The sorcery required to create dragon balls was only given to the peaceful and responsible people of Namek originally, but one of the Namekians escaped to Earth during the cataclysm and created more there. The 'original' dragon balls were connected to the life-force of The Great Elder, until his passing when Muri re-created them. Kami-Sama and by extension Piccolo were connected to the Earth Dragon Balls, but this ended when Piccolo assimilated Kami-Sama and they were re-created by Dende.