Nebula gas refers to the clouds of gas and dust found in space, primarily composed of hydrogen and helium. These clouds are often the birthplace of stars and planets, as they provide the necessary materials for stellar formation. When regions within a nebula become dense enough, gravity can cause the gas to collapse, leading to the creation of new celestial bodies. There are different types of nebulae, including emission nebulae, which glow due to ionized gas, and reflection nebulae, which reflect light from nearby stars. Supernova remnants can also form nebulae, dispersing gas and dust into space after a star explodes.