Okay kiddo, so in some languages people write with different characters than we do in English. Korean is one of those languages. They use a writing system called Hangul, which is made up of letters that look kind of like our letters but are different.
But sometimes, Korean words need to be written in other languages, like Russian. And that's where cyrillization comes in.
Cyrillization is when you take words written in one writing system (like Hangul) and write them using a different system (like Cyrillic, which is what they use in Russian).
It might seem confusing, but imagine you have a toy that's made of blocks. If you take the blocks apart and put them back together differently, you can still make the same toy, just in a different way.
That's kind of like what cyrillization does. It takes the same words, but writes them using different characters.
So in the case of Korean words in Russian, people use a special system to change the Hangul letters into Cyrillic letters. This makes it easier for Russian people to read and write Korean words.
There are actually lots of different ways to do this cyrillization, so sometimes you might see Korean words written differently in different languages. But the basic idea is always the same: taking the same words, but writing them using different letters.