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"
Giant Emission Nebula NGC 3603 in Infrared
14/08/2002
NGC 3603 is the largest region of glowing gas in our Milky Way galaxy. Spanning over 20 light years across, the giant emission nebula (HII region) is home to a massive star cluster, thick dust pillars, and a star about to explode. NGC 3603 was captured above in infrared light by a Two Micron All Sky Survey (2MASS) telescope. The young star cluster near the center heats the region's mostly hydrogen gas. Many stars in the cluster are estimated to be about one million years old, much less than the five billion-year age of our Sun. NGC 3603 lies approximately 20,000 light years away toward the constellation of Carina.