Wikipedia offers some proposed theories, you can read them by following the link below.
a kingdom
mammal, rational biped
the kingdom of moral ends
'The Goblin Companion' gives a vague explanation of where the goblin kingdom used to be before it vanished. Some sort of labyrinth apparently. Note: it might be fictional
There was no Anime released for Kingdom Hearts, but as for in the games, he first appeared in Kingdom Hearts I.
The cast of Such Is the Kingdom - 1911 includes: Charles Herman as The Rector
The cast of My Kingdom for a Hearse - 1928 includes: Al Cooke
The cast of Kingdom Protista - 2000 includes: Sean Lock
The cast of Kingdom - 2012 includes: Masakazu Morita as Xin Li
The cast of Kingdom for a Horse - 1938 includes: Corey Thomson as Narrator
The cast of Kingdom of the Wild - 1947 includes: Knox Manning as Narrator
The cast of Kingdom of Ends - 2008 includes: Jim Lyke as Detective