Referring to one of the main villains of the game Final Fantasy VII. Jenova was according to the game a being from another world. The Cetra people called her or referred to her as "The calamity from the skies". Jenova was thought to be the underlying reason why many of the cetra died. Approximately 2,000 years after that time she was found by professor Gast in a "Geological stratum". Hojo of Shinra was the person who first began experimenting with the cells of Jenova Ultimately producing Sephiroth and his clones and setting in motion the events of Final Fantasy VII.
In the game Sephiroth was told that Jenova was his mother, but in reality it was Lucrecia. Sephiroth was the first human to be injected with Jenova's cells making him vastly stronger than any normal person.
Also known as mother, she is what Kadaj, Azu, and Loz were looking for in Final Fantasy Advent Children. Or as they said they wanted "mother's" head. Once Kadaj got his hands on the box or tin that held Jenova Cloud Strife was after him to get Jenova back to prevent Sephiroth from arising from his "memories".
Kadaj: Wheres Jenova (mother, he said mother...)?!
Tifa: theres nobody here!