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 Eagle Nebula from CFHT
13/02/2003
Bright blue stars are still forming in the dark pillars of the Eagle Nebula. Made famous by a picture from the Hubble Space Telescope in 1995, the Eagle Nebula shows the dramatic process of star formation. To the upper right of the nebula in the above picture lies the heart of the open cluster M16. The bright blue stars of M16 have been continually forming over the past 5 million years, most recently in the famous central gas and dust pillars known as elephant trunks. Light takes about 7000 years to reach us from M16, which spans about 20 light years and can be seen with binoculars toward the constellation of Serpens.