The first four planets are called terrestrial planets because they are rocky.

Irenaeus tells us: "the holy Hebdomad is the seven stars which they call planets" (i. 30).

Long before there were telescopes, astronomers or written history, people gazed up at "wandering stars" that later observers would call planets.

There are much bigger astronomical objects that we don't call planets, so it was either upgrade those or downgrade Pluto.

The acuteness of the early observers enabled them to single out the more important of the wanderers which we now call planets.

When that's not enough, someone will start calling them planets and galaxies.

Meanwhile there's a sphere of dust and fragments around each star; those fragments we call planets.

At least two more bodies were discovered later, and called planets:

(The Sun and Moon were sometimes called planets as well.)

It is occupied by numerous irregularly shaped bodies called asteroids or minor planets.