This article goes into great detail about the various methods that one can use to measure or calculate the orbit-clearing capability of an orbiting body.

It turns out that for all of these different methods, you will find an extremely clear bimodal distribution that groups the 8 planets together as being highly capable of clearing their orbits whereas everything else falls into a statistically distinct non-clearing group. This is because there's sound dynamic reasons for why objects would fall into one group or the other with nothing lasting long in the "grey area" between them. Once an object becomes significantly better than its orbital neighbors at clearing the neighborhood it snowballs due to the feedback loop of scattering or absorbing its neighbors into itself.

That makes this a good criterion for classification. As the old saying goes, "cleave nature at the joints."

There are so many nasty potential jokes I decided not to get involved. Fuck it I ain’t touching that with a 30-foot pole.

it means that either pluto isn't a planet, or basically the entire fucking asteroid belt it's part of is all planets