Nebula
A nebula is a giant cloud of gas (mostly hydrogen and helium) and cosmic dust situated between stars in the interstellar medium. Nebulae serve as sites of stellar birth and death—including emission nebulae that glow from ionized gas, reflection nebulae that scatter starlight, and dark nebulae that obscure background stars.
Source: science.nasa.gov
APODs including "Nebula"
The Orion Nebula in Hydrogen
22/11/2000
The Great Nebula in Orion can be found just below and to the left of the easily identifiable belt of three stars in the popular constellation Orion. This fuzzy patch, visible to the unaided eye, contains one of the closest stellar nurseries, lying at a distance of about 1500 light years. The above picture highlights red light emitted by the nebula's hydrogen gas. Dark dust filaments punctuate regions of this glowing hydrogen gas and reflect light from the nebula's brightest stars. Recent observations of the Orion Nebula by the Hubble Space Telescope have located solar-system sized regions that are thought to be planet-forming circumstellar disks.