From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Inside Boo (FUNimation "Inside Buu") is the inside of Super Boo.
Inside Boo first appeared when Super Boo absorbed Vegetto while the Saiyan Fusion was protected by his Energy Shield. The Potara Fusion did not support the environment inside Super Boo and was nullified. Separated, Son Goku and Vegeta explored the inside of Super Boo. They fought against Enzymes, a Roundworm family, illusions of Gotenks, Son Gohan, and Piccolo, and Super Boo himself, who had materialized inside himself. They then freed their friends and sons, as well as Mister Boo, from the inside of Super Boo before escaping his body.
Inside Boo was explored in Dragon Ball Z: Buu's Fury. Goku and Vegeta visited Super Boo's Stomach, Super Boo's Intestines, and Super Boo's Brain. Enemies encountered are Blood Cells, Blisters, Enzymes, and Roundworms.
It is named Bū no Tainai (ブウ の 体内, Bū no Tainai) in Dragon Ball Kai Miracle Battle Carddass.
- The area that leads from the stomach to Super Boo's brain is called intestines in Buu's Fury, but it should have been called esophagus to be consistent with regular anatomy.