Kerbin is a terra planet where Kerbals live.
It has green plains, tan-yellow deserts, brown-white mountains and blue oceans and is very similar in characteristics to Earth. On this planet, you will find the Space Center Kerbal Space Center. It is a complex society with facilites designed to pump rockets out of its atmosphere. Here is it's in-game description:
"A unique world, Kerbin has flat plains, soaring mountains and wide, blue oceans. Home to the Kerbals, it has just the right conditions to support a vast, seemingly undepletable population of the eager green creatures.
Reaching a stable orbit around Kerbin is one of the first things budding space
programs strive for. It is said that he who can get his ship into orbit is halfway to anywhere."
Copied from KSP Wiki.
This planet is in what is known at the System Kerbol System. It is a place which honors the very aspects of Earth.
Kerbin is known to be the 3rd planet in the Kerbol System. It has 2 moons named Mun and Minmus. Don't forget it also has polar ice caps too. You will find the planet in a game called Space Program Kerbal Space Program.
Kerbin is a unique place to stare at. It hold the glory of Earth in its very design.