Alright kiddo, let me try to explain the Khazar Hypothesis of Cossack ancestry in a way that you'll understand.
So, a long long time ago, there was a group of people called the Khazars. They lived in a place called the Khazar Khaganate, which was near the Caspian Sea. They were like a big tribe of people who each had their own jobs to do, like farmers, warriors, and traders.
Now, some people think that the Cossacks, another group of people who lived later in history, might have come from the Khazars. It's like how some people might say that they have ancestors who came from a certain country or area.
This idea is called the Khazar Hypothesis of Cossack ancestry. "Hypothesis" just means a guess that people are trying to prove or disprove. Some people believe in this hypothesis, while others don't.
Scientists and historians look at things like DNA, language, and history to try to figure out if the Cossacks really came from the Khazars. But it's not always easy to know for sure!
Does that make sense, kiddo?