A Kingdom consist off all the "worlds" in Super Mario Odyssey (SMO). Each Kingdom requires a certain amount of Power Moons to access it, the only exceptions are Cap Kingdom due to the lack of the Odyssey and Mushroom Kingdom gets unlocked after beating the game. Cloud Kingdom and Ruined Kingdom need a certain amount of moons to reach the kingdom but are not exactly intended on going to the Kingdom, more forced to go. There are a total of 17 Kingdoms in the game and only 14 are in the main game, the other 3 are unlocked AFTER the main game.

This is the list of all the Kingdoms.
Darkest Side Isle Delfino
Kingdom Total Moons (at least)
Cap 31
Cascade 40
Sand 89
Lake 40
Wooded 74
Cloud 2
Lost 35 (default)
Metro 81
Snow 55
Seaside 71
Luncheon 68
Ruined 10
Bowser's 62
Moon 124
Mushroom 38
Dark Side 24
Darker Side 1
45
30

(PS. If I made any mistakes, please fix them, thanks.)