A Universe (宇宙, Uchū) is a singular collection of body of organisms and phenomena that contains the structure of the Dragon Ball series' set of universes. A universe is divided into normally halves but contain sets of realms that exist beyond these two halves, where its divided to various sections that include various planes of existence that are one sole collective. In the start of the series there was only one known to have existed, where Beerus later informed Gokū there was Twelve Universes,.
The Dragon Ball series' universes are divided between three large areas, the Living World, the Kaiōshin Realm and the Other World. Each of which have relationship between regulating the other planes.
Main article: Living World
The Living World (この世, Konoyo; Literally meaning "Present World") is the vast universe that contains the divided galaxies of the Universe, Each of which are divided into four cardinal directions that are each monitored by the Kaiō. The mortals of this plane are able to travel through the vast universe, but cannot freely travel the Afterworld, unless they die which they are turned into souls upon death. However there is some who are given permission to travel by the Gods of the Afterworld.
Main article: Afterworld
The Afterworld (あの世, Anoyo; Viz "Other Side"; Literally meaning "World Beyond") that is also referred to as the Cosmos (天界, Tenkai; Literally meaning "Celestial Sphere") a spiritual world that is is the world after death, where the Souls that have lost their physical bodies exist. The spiritual plane is divided between three sections where the gods who govern the entire Universe reside. The realm is monitored by the Kaiōshin.
Creation and Conception
When imagining the universe, Akira Toriyama thought of it as a sphere because it would be easier for himself and his readers to grasp. Later, he claimed that he invented his own universe, without using any references, because it was easier on him.