Half World
from Fancyclopedia 2 ca. 1959
(Heinlein:Burbee) The LASFS. In Heinlein's Magic, Inc the Half World was the domain of, uh, nature inhabited by demons, spirits, gnomes, fairies, ktp. The Insurgents used the designation in contempt for the LASFans' retreat from life, but the modern revived group in LA uses it in humorous self-designation.

from Fancyclopedia 2 Supplement ca. 1960:
The LASFS used this in humorous self-designation even before Burb and Laney, who picked it up from them.