Okay kiddo, so a khagan is a really special word that comes from a long time ago in a place called Central Asia. It was a word that meant a really powerful ruler or king who was in charge of lots and lots of different tribes that lived in the same area.
You can think of it like being the leader of all the kids in your class or on your block, but instead of just one group, the khagan is in charge of many different groups of people called tribes.
The khagan was really important because they helped to keep all the tribes together and prevent them from fighting with each other. They were kind of like a big boss or a captain of a ship, making sure everyone was working together towards the same goals.
Sometimes, a khagan would be really strong and powerful, and they would even conquer other places outside of Central Asia. Some people even thought of them as being like a god because they had so much power and control over so many people.
So that's what a khagan is, a really important leader who was in charge of lots and lots of different tribes in Central Asia a long time ago.