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"
Reflections Of Orion
15/01/1999
The Orion Nebula and its surroundings present skygazers with a wondrous jumble of newborn stars, gas, and dust. Emission nebulae - glowing energized clouds of gas, and reflection nebulae - dust clouds shining by reflected starlight, abound at this photogenic cosmic location a mere 1,500 light-years or so away. This telescopic image reveals an intriguing nebulosity which seems to consist of dust clouds illuminated not by starlight but by the light of the Orion Nebula itself. In non-telescopic views, the bright group of stars near the top appear as the northernmost star in Orion's sword. They are seen here illuminating the nearby dust clouds. Yet the yellowish streamers of dust across the middle reflect the light of the Orion Nebula, which lies just off the bottom edge of the photo.