Majin Boo's Cocoon
From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Majin Boo's Cocoon (魔人 ブウ の 殻, Majin Bū no Kara; Literally meaning "Majin Boo's Shell") is the object that Majin Boo is sealed within by Bibidi until Babidi and his possessed warriors, Dabura, Puipui, Spopovich, Yakon, and Yamu help release him.
Majin Boo's Cocoon was hidden at the bottom of Babidi's Spaceship. After Spopovich and Yamu drained the energy from Son Gohan at the Tenkaichi Tournament, Babidi almost had enough energy to revive Majin Boo. Using the energy from his warriors on his spaceship, he was able to gain enough power to awaken the deadly Majin.
It is named Majin Bū no Tama (魔人 ブウ の 玉, Majin Bū no Tama) in Dragon Ball Carddass Hondan.