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"
A Chamaeleon Sky
09/06/2002
A photogenic group of nebulae can be found toward Chamaeleon, a constellation visible predominantly in skies south of the Earth's equator. Celestial objects visible there include the blue reflection nebulas highlighted by thin dust surrounding the bright stars in the above image center. Toward the top and lower right, dark molecular clouds laced with thick dust block light from stars in the background. The parent molecular cloud Chamaeleon I is located about 450 light years from Earth.