Luna is the scientific and official name of The Earth's moon. The Society most probably started using the name after colonising other planet's moons. Part of the Core of the Society. Many locations depend on trade with Luna to exist. Its air was described as being stuffy and cloying. The gravity is 1/6 of Earth's, so structures can be made a lot higher. Sometimes factories are built on top of old factories. Large acres of land in the Citadel were used to house the villas that other Houses would stay in for the duration of the Summit.