Okay kiddo, imagine you have a piggy bank where you keep all your money that you've earned. When you move to a different country, the government of the country you used to live in might want to take some of the money you earned while you lived there as a "goodbye" gift. They call that "expatriation tax".
Now, imagine you have a special type of piggy bank that is worth a lot of money – like a treasure chest. If you decide to move to a different country and take that treasure chest with you, the government might want to take even more money from it as an expatriation tax. This is to make sure that you have paid all the taxes that you are supposed to pay before you leave and take your treasure with you.
It's important to know that not everyone has to pay an expatriation tax. It usually only applies to people who are considered "rich" or who have a lot of money in their piggy bank. So, if you are planning to move to a different country, make sure to talk to an expert who can help you understand if you need to pay an expatriation tax or not.