Let's really simplify things
If a world is as big or bigger than Mercury and not circling something larger
than itself (excluding the Sun, of course), then it's a planet.
If it's smaller, it's a planetoid or a comet or a space rock, but not a major planet.
So we have 8 major planets - 4 terrestrial worlds and 4 gas giants. The rest
are so much flotsam, some of which got lucky enough to be round and have
some interesting features, but they are not major planets.
There, everybody can go home now.