"Dragon Balls" are entirely fictitious objects possessing supernatural power, and they are not found in real life. They come from a Japanese comic book created by Akira Toriyama called "Dragon Ball."
In the series, there are seven Dragon Balls on each planet. When they are all collected, a magical dragon grants the person who gathered them a wish. Because the manga was originally published in serialized form, Toriyama decided to give the heroes a game-like activity of gathering something. Toriyama has stated that he chose the number seven because it was one less than the number of Samurai half-brothers in the 19th-century epic novel "Nansō Satomi Hakkenden."