Okay kiddo, let me explain what an uncountable set is.
Do you know what a set is? It's just a group of things. For example, I can have a set of toys which includes your teddy bear, your doll, and your toy car.
Now, let's say I have a set of numbers. I can count them, right? I can say 1, 2, 3, 4, and so on. These are called countable sets.
But there are some sets that are so big that you can't count them like this. These are called uncountable sets.
For example, think about all the possible decimal numbers between 0 and 1. That's a really big set, right? You can write down some of them like 0.1, 0.2, 0.3, and so on, but you can never write down all of them. That set is uncountable.
Another example is the set of real numbers. This includes all the numbers you can think of, like 1, 2, 3, pi, e, and even crazy numbers that you might not have heard of yet. This set is also uncountable.
So, an uncountable set is just a really big set that you can't count like you would with smaller sets.