Okay kiddo, so you know how sometimes there can be a disagreement between two people or groups about who owns or controls something? Well, that's kind of what's happening with Taiwan.
You see, Taiwan used to be a part of China a long time ago, but then some things happened (we don't need to get into that now) and now Taiwan is kind of on its own. But China still thinks that Taiwan belongs to them, and Taiwan thinks that they are their own separate country.
Now, most other countries in the world have decided to not pick a side and just say that they don't really know who Taiwan belongs to. That's what the theory of the undetermined status of Taiwan is - it means that nobody really knows for sure if Taiwan is its own country or if it belongs to China.
And because nobody knows for sure, things can be a little bit complicated. Some countries might do business with Taiwan like it's its own country, while other countries might say that it's a province of China. It's kind of like if you were playing a game with your friends and both you and your friend wanted to be in charge - it can be a little confusing and frustrating!
But don't worry too much about it, kiddo. The people who are in charge are grown-ups and they are working on figuring things out. Just know that there are some disagreements about Taiwan and that some people think it's a country and some people think it's a province of China.