The emission nebula known as IC 1396.
A nebula is a cloud of gas and dust in space. There are three general types: emission nebulae, which shine by their own light, reflection nebulae, which reflect light from nearby stars, and dark nebulae, which absorb light and appear dark against a brighter background.
When cloudlike material in space is patchy, or of a form that is difficult to categorize as a particular type of nebula, is referred to as nebulosity.
Originally, the term "nebula" (a Latin word meaning "mist") was applied to a variety of extended objects in the sky, including what are now known to be external galaxies; for example, the Andromeda Galaxy used to be, and occasionally still is, called the Andromeda Nebula.