A Planetary Nebula (PN or PNe) is ionized gas around an Asymptotic Giant Branch star. The term stems from the era of their first observation since given the observation methods of the time, they resembled planets.
They are presumed to live on the order of ten thousand years.
Vorontsov-Velyaminov Planetary Nebula Types:
Protoplanetary Nebula (PPN)