[Beowulf9]

Definition of a planet: a planet is a body that orbits the Sun, is massive enough for its own gravity to make it round, and has “cleared its neighbourhood” of smaller objects around its orbit.

So how is Pluto not a planet?

[naturalman1975]

Definition of a planet: a planet is a body that orbits the Sun, is massive enough for its own gravity to make it round, and has “cleared its neighbourhood” of smaller objects around its orbit.

So how is Pluto not a planet?

It doesn't meet that third criteria that I've bolded.

[Moonman62]

So how is Pluto not a planet?

...

The decision to make Pluto a dwarf planet was made by a small group of astronomers (not planetary scientists) and their criteria were arbitrary. Planetary scientists seem to have an issue with it.

[MadMax, the Grinning Reaper]

Looks like my stomach ulcer. I have an alien world in my stomach. Who knew? Gotta chance my meds.

[coloradan]

Pluto’s orbit is also significantly tilted relative to the orbits of the (major) planets. Plus, if Pluto were a planet, a few hundred other objects would also be planets, some of which are much smaller than it is, and which incidentally also haven’t cleared their orbits of things, just like Pluto hasn’t.