Boo World is a theme park on Earth created by Mister Bii in honor of Majin Buu who had healed his blindness during the Majin Buu conflict in Age 774 when Mister Bii was just a boy. The park is run by mostly Majin employees. Boo World appears in Dragon Ball Online.
During the Majin Buu conflict, Majin Buu encountered a young blind boy named Tommy who did not flee from him which confused Buu as people normally fled in terror from him. Learning of the boy's blindness made him unable to see Buu, the innocent Majin used his healing powers to cure Tommy's blindness. However the boy was not frightened of Buu as he had never seen another person before thus did not know who he was. Tommy thanked him and even complemented him which pleased Buu who spared the boy's life and even gave him some milk (which unbeknownst to Tommy had been a man whom Buu had turned into a carton of milk).
Tommy later died during the conflict along with most of Earth's population. However, as he was a good hearted boy, Tommy was revived by Porunga retaining his sight which had been restored before his death and was unrelated to his manner of death. Most of the Earth's population would forget Majin Buu's evil rampage due to a wish to Shenron made by the Z Fighters to give Good Buu a second chance as he had fought to protect his friends Mr. Satan and Bee from Kid Buu. However Tommy was ignorant of who Buu was at the time and since his encounter with Buu was a positive one, his memory was unaffected as Shenron apparently only erased memories of Majin Buu's evil as per the spirit of the wish which was to allow Buu to start over and live in peace. Good Buu became Mr. Satan's official pupil whom Mr. Satan convinced the Earth's population was a space warrior who had sought out Mr. Satan for training as a cover story to explain Buu's presence and origins as most of the Earth's population did not remember Buu. However Tommy did and felt beholden to Good Buu for restoring his sight. Meanwhile Mr. Buu used fission to create a female companion Miss Buu whom became his wife and had a child a year later. Before long their family grew resulting in the beginnings of the Majin race. Tommy eventually changed his name to Mister Bii and worked heard building a fortune which he used to establish a his theme park Boo World in honor of Majin Buu. He also provided employment for many Majin to the point that the park mostly consisted of Majin employees.