Astronomers use the term nebula to refer to
a) outer envelopes of dying stars that drift gently into space.
b) remnants of stars that die by supernova.
c) clouds of gas and dust in interstellar space.
d) distant galaxies seen beyond our Milky Way.
e) All of the above are correct.
Answer: e) All of the above are correct.
Nebula refers to any fuzzy patch - bright or dark - in the sky.