Earth (also known as the Dragon World) is a fictional planet, (based on a non-fictional planet) inhabited by humans, demons, extraterrestrials, and the like being the main setting for the bulk of the plot of the Dragon Ball manga, the Dragon Ball anime, Dragon Ball Z, as well as Dragon Ball GT. It is also the setting for two other manga by Akira Toriyama: Dr. Slump and Neko Majin Z.
Politically, Earth has a planet-wide monarchy. It is divided into 43 "sectors", led by the King of the Earth. The dating system is also quite different. While the length and divisions of the year seem to be identical to the Gregorian Calendar, years are reckoned by the Age system (エイジ Eiji, interpreted as the Christian A.D.). The standard currency is Zeni, which is mostly mentioned at the Tenkaichi Budokai.
With the exception of most of the notable characters in the series, most of Earth's inhabitants seem to suffer from Sunnydale Syndrome. Despite the obviously staggering power of Goku and the other Z Fighters, most of the populace believe Hercule to be the world's strongest fighter. They continue to believe this even after several pathetic losses to various foes, due in part to Hercule's ability to convince them that his opponents cheated somehow or he let them win. Even when directly confronted with evidence directly contradicting Hercule (and even when he is clearly absent from the battlefield), they continue to believe him responsible for many of the major victories in the series, although the Z Fighters (after accepting Hercule as one of the group for his part in defeating Majin Buu) later use this to their advantage to avoid becoming the center of attention.
In the Dragon Ball universe, all planets benefit from an appointed deity. Throughout most of series, the God of the Earth (Guardian of Earth in the English dub) is Kami, but later that position was given to Dende after Kami had merged with Piccolo. Because both Kami and Dende are Namekians, they have the ability to create the seven Dragon Balls, which can grant wishes if all seven are collected. These wishes are used regularly throughout Dragon Ball for many various things, usually bringing people back to life. Earth itself is wished back into existence a number of times through this method.
When compared to other species of Dragon Ball, humans are significantly weak. It is said that a single Saiyan infant would be capable of destroying the general population on its own. However, a select few humans have learned to use chi and are among the strongest beings in the universe. Even with such abilities, this select group of humans are still considerably weaker than many aliens with the same chi-manipulation abilities. As stated in the manga, it's possible for any human to use their chi and gain powers like the Z Fighters. For example, Gohan easily teaches Videl how to use chi to fly.
Though less common, intelligent anthropomorphic (and sometimes non-anthropomorphic) animals such as Oolong and Puar are integrated into the population and are well-adjusted and are also accepted as people (this is similar to fairy tale animals in European fiction, such as the Three Little Pigs, Puss in Boots, etc.). Even so, the anthropomorphic population sees a drastic and noticeable decline over the course of the series.
Creatures and devices used on Earth also vary greatly, as is common in works such as Dragon Ball. Dinosaurs and other extinct creatures in the real world still roam the Dragon World freely, while the characters fly around in futuristic levitating cars and houses that can be shrunk down to convenient travel-sizes.
The tournament is fought on an outdoors arena, with the preliminaries fought inside the main building. Weapons and protective gear are forbidden and result in immediate disqualification, as does killing an opponent. The matches are won either by knockout, surrender or knocking an opponent out of the ring. Little is known about the tournaments prior to the 21st, which is the first one shown in the series, although several winners are mentioned at different points. The demonic Akuman is mentioned as having won it twice. Notable winners include Master Roshi (21st), Tien (22nd), Goku (23rd), and Hercule (24th).
Originally, the Budokai is said to occur every five years, though after Goku's participation in the 21st tournament, the inbetween time is shortened to three years, due to a surge in popularity by the people. However, after the arena is destroyed during Goku and Piccolo's battle in the 23rd tournament, the inbetween time appears to change, because the 24th tournament that Hercule won, which is never shown on screen, is never mentioned as to how many years it took place after the 23rd. As time goes on the 25th tournament occurs seven years after the Cell Games, which took place more than ten years after the 23rd tournament. The final Budokai to take place in the manga is the 28th, which takes place ten years after the battle with Majin Buu.
The owner, Korin grows , a kind of mystical bean that completely replenishes the consumer's health and energy, in the tower, which he gives to the Z Fighters freely. Their texture is said to be a cross between an uncooked (or under ripe) bean and a celery stalk. The Senzu beans' healing capabilities have been able to perform such feats as healing a hole in a character's chest and restore fatally injured characters to perfect health in various occasions. The beans are extremely powerful, however they are not capable of curing sicknesses or ailments such as the heart virus Goku contracts during the Android invasion. It was stated that eating one bean is equivalent to ten days worth of food. They are often carried in small sacks during fights as a safety measure.
The somersault cloud, , also belonged to Korin, who gave it to Master Roshi when he had climbed Korin Tower. Roshi used this cloud in his youth, when he was pure of heart and before his obsession with women. A couple hundred years later, Roshi's pet turtle was lost on the main land and returned to the sea by Goku. Roshi gives this cloud to Goku as a token of his appreciation, however when he attempts to demonstrate the standards of the cloud to Goku, he is unable to sit on it due to his impurity of heart because of his lust for women. Goku uses the cloud for travel extensively throughout Dragon Ball, though by the middle of Dragon Ball Z, he stops using it due to his mastery of flight on his own. In the English dub, the cloud is known as the Flying Nimbus.