The Mega Society was founded in 1982 by Ronald K Hoeflin to facilitate psychometric research. It’s a high IQ society for those who have scored a one-in-a-million level on a test of general intelligence claimed to be able to discriminate at that level. Those who get in the Mega Society are in the 99.9999th percentile on the IQ test. The current administrator of the Mega Society is Jeff Ward.
Mensa, the best known IQ group is open to one person in fifty. Mensa is the largest and oldest high IQ society in the world. It was founded in 1946 as a non-profit company in England and is open worldwide. There are about 110,000 members of the Mensa Society. So, yeah, the Mega Society is ultra elite in comparison.
After taking the IQ test, you still have to take the Mega test to get into the Mega Society. It is for the ultra-mega-elite of intelligent people.