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 Great Nebula in Orion
27/09/2004
The Great Nebula in Orion is a colorful place. Visible to the unaided eye, it appears as a small fuzzy patch in the constellation of Orion. Long exposure, digitally sharpened images like this, however, show the Orion Nebula to be a busy neighborhood of young stars, hot gas, and dark dust. The power behind much of the Orion Nebula (M42) is the Trapezium - four of the brightest stars in the nebula. Many of the filamentary structures visible are actually shock waves - fronts where fast moving material encounters slow moving gas. The Orion Nebula spans about 40 light years and is located about 1500 light years away in the same spiral arm of our Galaxy as the Sun.