A Dragon Ball is a fictional artifact from the manga and anime Dragon Ball/Dragon Ball Z, as well as Dragon Ball GT. They also appear in the Akira Toriyama manga Dragon Boy (the proto-Dragon Ball one-shot series).

Dragon Balls in "Dragon Ball" series

The Dragon Balls are orange glass-like spheres with the ability to call forth a massive dragon, which has the ability to grant wishes. Dragon Balls come in sets of seven with each ball containing the number of stars that signifies its respective number in the set. Dragonballs are difficult to find because they are scattered all over the Earth and deactivated for a year after every wish, so to have the opportunity to summon a dragon one must travel all over the globe to retrieve them.

Unlike the Dragon Balls of Earth, the Dragon Balls of Planet Namek summon a different dragon Porunga and can grant three wishes. Since the years on Namek are shorter, they can also be used more frequently. The balls are also about twice the size in diameter as the balls on Earth. Comparatively, think of the Earth Dragon balls as Baseballs, and Namek Dragon Balls as Basketballs

In Dragon Ball GT, "Black Star Dragon Balls" are introduced. This special set of Dragon Balls feature black stars (as opposed to dark orange ones) and can call forth a dragon with the ability to cast any wish, with no power restriction. After a wish has been cast with the Black Star Dragon Balls, the balls are scattered across the universe (rather than planet)and if they are not collected again with in one year, the planet the wish was cast on will explode.

Dragon Balls in "Dragon Boy"

In the manga Dragon Boy, Dragon Balls are small balls that appear very similar to the balls in the Dragon Ball series. However, instead of granting wishes, they can be opened using ki energy to release a small baby dragon that does not grant wishes.