Nebulae
Historically, the word nebula was used to describe any diffuse, glowing object in the sky, including distant galaxies. We now understand them to be illuminated clouds of gas and dust, energized to glow from nearby starlight that excites the gas within them.
Some nebulae are associated with the birth of stars: the so-called star forming regions, or HII regions (pronounced “H-two”). The misnomered planetary nebulae form in the late stages of some star’s lives (and have nothing to do with planets). And, supernova remnants are the left over ejecta from a supernova explosion—the dramatic end-of-life stages for massive stars.