Kami (Dragon Ball)
Kami is the name for two things from the Dragon Ball universe.
The title of Guardian of the Earth (the word literally translates to "God"). For a person to become Kami, one must a) be worthy, and b) have a pure good heart. Though a person may have good ambitions to become Kami, that person's heart may have a bit of evil. So they must have a purification ceremony to. A person does not have to be born from Earth to become Kami, like the Namek noted below.
The pure half of the original Namek. Hundreds of years ago, the Namek who had forgotten his origins was chosen to succeed the former Kami as the new Guardian of Earth. However, this Namek who called himself Piccolo was impure, and could not rise to the throne until he could cleanse his soul. The process of purifying Piccolo's soul actually cause him to literally split into two seperate beings equal in wit and power. His dark half, who came to be called Piccolo Daimaou (or the Great Demon King Piccolo, and his pure side, who refers to himself only as Kami-sama. The two had a spiritual link, and so technically they're still the same original entity. When Goku killed King Piccolo, Kami survived because King Piccolo spit out an egg before he died.
During the Imperfect Cell Saga, Kami and Piccolo fused together and become the "Namek with no name" before he split into Kami and Piccolo Daimaou.
It's not known whether Earth isn't the only planet with a Kami. As King Kai tells Goku during his training that the Kami of Planet Vegeta, disgusted with the Saiyans, summoned a field of meteors towards their world and destroyed them. Of course, he lied so that Goku would run into Frieza if he knew the truth.
It is suggested that Kami's actual name was "Piccolo," during his earlier days on Earth.