A nebula (Latin: “mist”; pl. nebulae or nebulæ, with ligature; from Greek nephele, “cloud”) is an interstellar cloud of dust, gas and plasma. Originally nebula was a general name for any extended astronomical object, including galaxies beyond the Milky Way (some examples of the older usage survive; for example, the Andromeda Galaxy is sometimes referred to as the Andromeda Nebula).