Universe Today
"A planet is a sub-stellar mass body that has never undergone nuclear fusion..." - part of the new planetary definition proposed by Runyon and his team.
Emphasizes intrinsic as opposed to extrinsic properties.
Can be paraphrased for younger students: "Round objects in space that are smaller than stars."
The geophysical definition is already in use, taught, and included in planetological glossaries.
There's no need to memorize all 110 planets. Teach the Solar Systems zones and why different planet types formed at different distances from the Sun.
"It is official without IAU approval, partly via usage." - Runyon and team, on their new definition.