Nebula/ˈnebjələ/ Definition 1 of 2Pro Tip 1/3Astronomy Context Understand 'nebula' is mainly used in astronomy; not common in daily speech. My favorite photo taken by the telescope is that of the Orion Nebula. Pro Tip 2/3Space Structure 'Nebula' is specific to space; don't confuse it with any Earth-based phenomena. The Crab Nebula was formed by a supernova explosion. Pro Tip 3/3Metaphorical Use Sometimes used metaphorically to describe something vague or indistinct. His explanation was a nebula of abstract concepts.