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"
NGC 5189: A Strange Planetary Nebula
11/12/1995
After a Sun-like star can no longer support fusion in its core, the center condenses into a white dwarf while the outer atmospheric layers are expelled into space and appear as a planetary nebula. This particular planetary nebula has a quite strange and chaotic structure. The inner part of this nebula contains an unusual expanding ring of gas that we see nearly edge-on. The exact mechanism that expels the planetary nebula gas is a current topic of astronomical speculation and research.