Related if more whimsical 2015 thread: What a planet is, revisited. Also Pluto, where I propose this definition, “A planet is a near-spherical object orbiting a star which has undergone planetary differentiation and is not a star or a brown dwarf.”
Click the link to read informed objections and commentary, for I am not an astronomer. Also I posted: “ISTM that we’re defining a term inclusive of apples and hub caps while ruling out strawberries. Not that this is a huge issue: Phil Plait speaks for many when he asserts what matters are the properties of Pluto, not what label we stick to it. For this general interest message board though, it’s not a bad entry point to planetary science.”
Lemur866 and more recently Chronos argue for the following: