REALM – A kingdom or a particular batch of kingdoms in the same general region.
LAND – A dimension/world within the multiverse.
So Fairytale Land is a LAND, while Agrabah and the Enchanted Forest/Mist Haven, are realms within it that contain separate kingdoms within them. Also, Oz would be a land, and the Emerald City is a kingdom within it.
So our world, the Land Without Magic is a land (obviously) and the different continents are realms (mmkay) and the countries within them are “kingdoms”. Okay…I think I got it. Maybe. I don’t know where my train of thought even is anymore.