Genii is the plural form of genie. Genie is the English version of the Arabic jinn, a supernatural creature in Arabian mythology and Islam. In English it is sometimes mistakenly translated as ghost.
Genie is a French word which refers to any kind if spirit. The word was originally derived from the Latin word genius which is a guardian spirit assigned for every human being at the time of birth.
Hebrews thought of genii as the spirit of vanished people from ancient times, who were nocturnal and would disappear with the first light of dawn. They were believed to be the culprits in causing many diseases and mental abnormalities in people. Some believed that jinn could possess anybody's body and soul and take control of them.
In Islam, jinn were believed to be creatures which had complete freedom and were made by God with smokeless fire. They are supposed to have their own families and do everything like humans. They can either be good or bad.
Genii have been portrayed as both good and bad in Western culture. Alladin's genie remains a favourite.
Genii are sometime called jinx. Jinx is a curse placed on people which brings bad luck to them. Genii are said to be the spirits bringing bad luck. When a person talks over-confidently about future events, it is said he tempts fate and the statements he makes act as jinx.