The term micro-g environment (also µg, often referred to by the term microgravity) is more or less a synonym of weightlessness and zero-g, but indicates that g-forces are not quite zero, just very small. The symbol for microgravity, µg, was used on the insignias of Space Shuttle flights STS-87 and STS-107, because these flights were devoted to microgravity research in low Earth orbit.