Answer: Name

In 2006, the celestial object previously known as the ninth planet in our solar system, Pluto, was officially demoted. Although the announcement by the International Astronomical Union left a lot of people scratching their heads and more than a few declaring, “It was a planet when I learned the solar system as a lad and it’s going to stay a planet!” the IAU actually had a rather compelling case. At the time the object was discovered in 1930, it looked unique and planet like. After nearly a century of astronomical study since, however, it’s clear that the object we called Pluto is but one of many numerous icy objects orbiting the Sun at similar distances (including another that is bigger than Pluto).

Part of the demotion process from planet to dwarf planet, while strictly a matter of bookkeeping and consistency in records, has a bitter twinge to it you’d expect to find in a tragic story: Pluto was stripped of its name and given a number like all the other asteroids, icy bodies, dwarf planets, and other chunks of non-planetary objects rocketing around the solar system. Pluto was reclassified and renamed with the designation 134340 along with all of its moons, also stripped of their names and reclassified as 134340 (I-V).

Despite the demotion and the stripping of title, Pluto lives on: members of the very class of planet it belongs to, that of the trans-neptunian dwarf planet, are referred to as Plutoids.